Ah, the comic book cover. There is something unique about the cover that stands out, sometimes more than the content of the book! In fact, there's a whole market for stylish variant covers done by guest artists.

RELATED: 15 Glaring Stereotypes In Comics History

However, there are some covers that irk or insult more than inspire. This is especially true of the comics of yesteryear, which had to be incredibly sensationalized and bizarre in order to sell. Since then, many covers have more-or-less turned into glorified pin-up pages and standalone images that may or may not relate to what's happening within the books.

Don't get us wrong -- artistic freedom is great, but there are times when decisions are made that rustle a few jimmies unnecessarily. We at CBR are fascinated by these beautiful train wrecks, and have decided to compile some of the most notorious covers to ever hit the shelves.

15 Sex Criminals' Variant Covers

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It's kind of amazing that Matt Fraction and Chip Zdarsky's ongoing series "Sex Criminals" gained the acclaim that it did. The topic of sexuality in fiction as a whole (especially in comics) is something of a hairy topic for many, but we've been pleasantly surprised with Zdarsky and Fraction's view of sexuality in this urban fantasy noir. It's also brought in some fantastic variant covers. Perhaps the biggest head-turner among the covers featuring art from commissioned illustrators was the variant by Scott Pilgrim creator Bryan Lee O'Malley.

It was... overt, to say the least. Featuring some full-frontal nudity, which looks really weird in O'Malley's cartoonish art style. We are also treated to a huge phallic goombah from Super Mario Brothers. So that happened. We shouldn't be too surprised. This is a comic about sex, after all, and it's by Zdarsky and Fraction. Still, we hope Nintendo didn't see it.

14 DC's New Teen Titans # 1

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Right off the bat, we've got a lot to unpack with this one. Long-time readers will remember when former DC editor Janelle Asselin did a big take-down of the cover for "DC's New Teen Titans" when it came out. To summarize the key points, there is a sexualized teen girl on the front cover with what look like silicone implants, a hugely distracting signature between said teen girl's legs and very bizarre placement and framing of each of her teammates. All this was done with an incredibly dated and unflattering art style ripped from the dark and pungent corners of '90s "Cool."

Unfortunately, certain ill-tempered fans took umbrage with the claims Asselin made, to the point that they bombarded her with threats of violence. Obviously, we know that many of our readers are good people and we do not believe in harassing people over comic covers (particularly ones about sexualized teenagers), but as we'll see these are not exactly isolated incidents. Case in point...

13 Riri Williams

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Not too long ago, Marvel announced that the character who will take up the Iron Man mantle will be a 15-year-old genius girl named Riri Williams, who calls herself "Ironheart." This is pretty exciting, as it's always interesting to see new characters step into the spotlight. Marvel's been marketing the character up and down when they can and people have been pretty graceful about her inclusion into the Marvel universe -- except for one thing.

Riri's outfit of choice seems to be a pair of black tights and a sleeveless belly-shirt, such that every artist seems intent on putting extra details into her appearance. This, of course, is incredibly weird for many readers because, well, she's technically a child. J. Scott Campbell's cover for the first issue of "Invincible Iron Man" is the latest contribution to this trend. Whatever justifications people make regarding the hows and whys of the stylistic decision -- i.e., that real teenagers wear this kind of style and many youngsters share Riri's body type --  don't quite change the fact that it's uncomfortable seeing a teenager sexualized in such a way.

12 My Ward Is A Junkie!

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Starting from the 1970s, superhero comics often tackle major social issues as a way of introducing them to their readers. Largely, these feel like Public Service Announcements, but there were times when it worked.

Perhaps the biggest shocker and most popular example is this cover for the 1971 Green Lantern/Green Arrow crossover story, "Snowbirds Don't Fly." In the book, Green Arrow enlists the help of Green Lantern to track down his ward Speedy, who became addicted to heroin and had been pawning some of Arrow's weapons to get his fix. The two-part story marked a moment when DC would focus on sociopolitical problems, particularly with Green Arrow.

Following the old-school model of using eye-catching covers to draw in readers, the cover for the first part of "Snowbirds" dropped a few jaws. The picture of Speedy sitting slouched in front of a plate of heroin with a syringe hit home for some and shocked many others. The book was praised as a success for years, however, and despite the controversial cover, has achieved an almost legendary status.

11 Silver Age Lois Lane's Bizarre Adventures

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The Silver Age of comics came with a certain level of weirdness that is as charming as it is bizarre. This was best exemplified by books like the Lois Lane series in "Superman's Girlfriend: Lois Lane." The covers for this serial ran the gamut of bizarre fantasies and scenarios featuring the plucky reporter, with covers for each series showing situations where she marries Batman or Jimmy Olsen, or turns into a centaur. As the series went on, it continued to explore weirder and weirder territory. Strangest of all was one issue where the cover shows Lois Lane turning into a black woman, saying that she has to live as a person of color for 24 hours.

Sure, this cover in particular is pretty bizarre, but there's an angle to it that makes us uncomfortable -- namely the implied blackface and the fact that the team who worked on the issue treated being black like some kind of sci-fi scenario on par with spending 24 hours as a mermaid.

10 Heroes For... Hentai?

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Before renowned Japanese illustrator Sana Takeda got to work on the stunning fantasy series "Monstress" with Marjorie Liu, She was attached to several projects with Marvel. Not only did she provide interior illustrations for books like "Ms. Marvel," she also created her fair share of covers for a number of books. Takeda's style was a welcome change for many fans as a breath of fresh, if often grave air.

However, the cover she did for a particular issue of "Heroes For Hire" made quite a few people squeamish. The cover for issue #13 featured Misty Knight, Black Cat and Colleen Wing being menaced by The Brood, chained to a post and having dripping tentacles reaching for their exposed flesh. Yikes.

Needless to say, the implied tentacle porn on the cover left a bad taste in a few peoples' mouths. Readers tried to rationalize it by saying "Yes, but the artist's a woman," but even that didn't exactly take away from the ick-factor for many.

9 Batgirl's Killing Joke

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Barbara Gordon's return as Batgirl in the new DC comics was met with considerable praise. Despite Stephanie Brown and Cassandra Cain bringing in a lot of attention and fans, it was Gordon's recovery and retaking of her old mantle that was a huge moment for readers. This is especially true since her unexpected retirement came from one of the most controversial moments in Batman history -- the Joker crippling Barbara during Alan Moore's infamous "Killing Joke" storyline. Despite its popularity, many -- including Moore himself -- would condemn the story as an ongoing campaign against female characters.

Then, in issue #41 of "Batgirl," a variant cover by Rafael Albuquerque was released showing Barbara being held captive by Joker in his classic "Killing Joke" outfit, as he paints a smile on her terrified face. Readers criticized the cover for bringing up this troubling moment in the character's history while unnecessarily showcasing sexual assault, while their opponents cried out for artistic freedom. It was a mess and tensions ran high throughout comics, to the point that Albuquerque would later request the cover be pulled after reading about the harassment and death threats his readers were getting.

8 Ultimate Twincest

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Plenty of comic fans enjoy reading about their favorite characters getting together. Some pairings are more popular than others and there are many who will fight to see these characters get together or stay together no matter what. Other pairings, particularly official pairings, are met with scorn.

Wanda and Pietro Maximoff -- AKA The Scarlet Witch and Quicksilver -- are one such pairing. Originally from Marvel's "Ultimates" line of comics, which was known for being very dark and weird, this ostensible "romance" between Wanda and Pietro was too much for some fans to take. The reason? They're twin brother and sister. Like... biological twin brother and sister.

This weirdness is especially hammered home with the cover of "Ultimates," issue #8. Here, we see Pietro and Wanda linking hands and looking lovey-dovey, and defensive, of one another. Very sweet! Still brother and sister, though. Great job, guys. Jaime Lannister would be proud.

7 Hansi

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This cover belongs to a one-shot comic written and drawn by Christian comics writer Al Hartley in 1973. "Hansi, The Girl Who Loved The Swastika" was a piece of historical fiction that condemned Nazi and Communist ideologies while promoting the teachings of The Bible. The story follows a young member of the Hitler Youth who eventually falls out of love with the Nazi party during World War II and defects to the United States, guided by her faith in God.

This cover is bound to make anyone whose families were victimized by the Nazis feel all kinds of uncomfortable. Of course, Germany actually banned Nazi symbology to the point where any piece of media featuring the swastika has to have the image scrubbed from the record, making this cover technically illegal there. It doesn't get much more controversial than that.

6 Ebony White

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As far back as we can remember, many of the early masked vigilantes in fiction were white Americans who had non-white sidekicks. The Spider had the Sikh assassin Ram Singh, the Green Hornet had Kato and the Lone Ranger had Tonto. It's hard to say how or why this trend started, but it's a trope we've seen time and again. Will Eisner's masked vigilante The Spirit had his own comrade in the form of African American youth, Ebony White, a long-time friend who even appeared alongside him on many covers. On paper, that sounds like a pretty neat idea...

Unfortunately, Ebony White was often depicted with offensive physical stereotypes, not to mention that he was drawn considerably smaller than The Spirit (in the early days, his age was not made clear) and was not nearly as well-dressed as his slick and stylish boss. Ebony's appearance would later be modified in future issues of The Spirit, but those early covers showing Ebony being overshadowed by The Spirit and stumbling next to him rubbed many readers the wrong way, and still do.

5 Slap A What Now?

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Speaking of racism, how about those jingoistic comic covers from yesteryear? With World War II raging on, so much media produced by the United States promoted the war effort in Europe. Comics showcasing heroic figures like Superman and Captain Marvel/Shazam socking it to Nazis and various leaders in the Axis forces were incredibly common. Unfortunately, since one of the Axis forces during WWII was Japan, and since many Americans were living in very divisive times, much of the rhetoric towards the country would be best categorized as stereotype.

Perhaps one of the most glaring examples of this is an issue of Action Comics where Superman is seen grinding out pamphlets promoting young Americans to "Slap A Jap." As if that wasn't enough, the picture of the ghoulish Japanese man on the pamphlet really sends a powerful message about how East Asians were viewed; which is to say, with physical stereotypes similar to those suffered upon Ebony White.

4 That Spider-Woman Stretch

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Milo Manara has been both popular and active in the European comics industry for years, perhaps best known for books like "Alessio" and "Il Gioco," also known as "Click." He also gained attention as an erotica artist, and has been making in-roads in the American comics industry for some time, even pencilling some issues of X-Men written by Chris Claremont. Since then, he's gone on to do some variant covers for different Marvel titles.

Although his art style is unquestionably unique, his cover for an issue of Spider-Woman kicked quite a few hornets' nests, as it depicted the title character on all fours, head craned upwards and in a position that nature show hosts would call "presenting." Also, her spandex looked extra tight on this one. Naturally, this led to a huge discussion between fans, with people debating whether or not the pose was too erotic. The kerfuffle turned out to be too much, however, and Manara's covers were cancelled.

3 Frank Cho

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Frank Cho is a comic artist best known for his work on Liberty Meadows, Mighty Avengers and Shanna The She-Devil. He has become a controversial figure in comics recently thanks mostly to his strong affinity for drawing voluptuous women, and his unbending resolve to troll.

Following Marvel's decision to pull Manara's "Spider-Woman" cover from the shelves, Cho decided to show solidarity for his fellow artist by recreating the pose in a sketch cover for Spider-Gwen. The fact that Spider-Gwen is a young college student brought a great deal of discomfort to some readers, but what more fans found offensive was that Cho made these covers with the express purpose of mocking the offended. So, mission accomplished then.

Some time later, the Manara pose was repeated again with a sketch cover for Wonder Woman. It went about as well as you'd think, with the art getting pulled, Cho sticking to his guns and many people on both sides angry.

2 Marvel's Hip Hop Album Covers

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Comic companies often try to connect with their audience, with comics creators showing their appreciation for other kinds of artists and mediums, as well as the affect one has on another.

Perhaps one of the most interesting examples of this has been Marvel's Rap Album variant cover series. Simply put, the covers in this series are all re-drawings of various rap album covers, only featuring Marvel characters. Want to see the Avengers recreate a Wu-Tang Clan album? Well, this is the series for you.

So, what's the problem? Well, the project drew some fire, not for the concept or creative ingenuity, but for having a dearth of black illustrators working on the series. Given that this was a genre of music popularized by black Americans, some creators and fans felt left out, stirring up discontent, not necessarily for the idea itself, but what was called its "tone-deaf" implementation of it.

1 Marvel's Prostate Cancer Covers

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In 2016, Marvel Comics decided to release a series of variant covers for their titles with the goal in mind to support those suffering from prostate cancer. Anyone who bought a book bearing the art and the special tag for prostate cancer awareness was donating money to cancer research.

Being that they were relatively tame -- only showing off a blue hue to the heroes' costumes -- the problem about these covers is that they are variants, meaning that not every book is going to have them. Secondly, retailers couldn't just buy the books with the special covers exclusively. They had to order the books en masse and then just hope for the best.

What's worse: there were reports that Marvel wasn't officially affiliated with any of the groups that actually support research for the disease, making this less an exercise in cancer awareness and research funding, and more one of brand marketing.

What were some comic book cover controversies that made you squirm? Let us know in the comments!