Stuck up, egotistical, and arrogant are all ways you could describe Flashy Flash from One Punch Man. He's a character that's supremely confident in his abilities, as most of the S-class heroes are. A lot of the time, he struggles to compliment anyone, more comfortable berating them for not training enough.
As with many heroes beyond Saitama and Genos, none of them have gotten an abundance of screen time in the anime as of yet— and even in the manga, it's still pretty low. No matter what form of media Flashy Flash is featured in, there are aspects of his character that instantly fall apart when closely examined.
10 The Depths Of His Arrogance
It's one thing to be a little full of yourself, as Flashy Flash is, even if it means talking back to Tatsumaki, the one hero just about everyone fears due to how strong she is. He even thinks he's stronger than her, once claiming she stole his kill. Where it gets a bit excessive is the fact he attacked Saitama, knowing that he too was a hero and then did it again because he couldn't come to terms with the fact Saitama managed to dodge his attack.
9 Able To Analyze Someone's Strength By Footstep
There are more than a few abilities in One Punch that are a bit over the top, but the fact that Flashy Flash can discern someone's physical attributes by hearing their footsteps (as he did to Saitama) is more than a little ridiculous. For one thing, that would take an incredibly acute level of hearing, especially with how specific he was in guessing Saitama's weight. It felt like a needless addition to his powers, as if having his high level of speed wasn't enough.
8 Getting Buried In Rubble
For all his speed and intelligence, Flashy Flash manages to get buried beneath rubble during Tatsumaki's battle with the fusion of Orochi and Psykos.
Much of this is because he couldn't be shielded due to his lost communicator, but it stands to reason that someone of his speed could avoid taking damage. Since the Flash isn't seen being covered in the debris of a falling building in DC comics, the same should hold true here. It feels like a cheap way of keeping him out of the fight.
7 Not Taking Opponents Seriously
Some of this is due to his arrogance, but the way he was so nonchalant with both the Hundred-Eyes Octopus and the monster duo of Gale Wind and Hellfire Flame is a bit inexcusable. He could have taken out both opponents with ease at the start of the fight— despite what he says— but instead chose to hold back like he was Goku.
That works for the Dragon Ball mainstay as he thirsts for a good fight. However, it doesn't really make sense for a character that thinks as highly of himself as Flashy Flash does.
6 Slaughtering The Whole Village
It's completely understandable why he felt the need to overthrow the current regime of the Ninja Village. They were evil and using kids to do their bidding, not caring how grueling the training was. Where things fall off the rails is that Flashy Flash killed everyone, be it instructor or student, leaving no one behind.
It's so similar to Itachi in Naruto, only the Uchiha made sure he killed everyone off save for his brother. Flashy Flash wasn't able to take out the prior generation, leading to the Heavenly Ninja Party.
5 Leaving Sonic Alive
Originally, taking control of the village was Sonic's idea, trusting Flashy Flash enough to tell him his plans. They were meant to do it together, letting the Ninja Village move towards a more benevolent leadership.
For whatever reason, Flashy decided to go against that, taking it upon himself to end the village, leaving it with no leadership. Presumably, Flashy left him alive for sentimental reasons, but that's pure speculation. It's never fully explained, and he seems more than willing to take Sonic out when they battle in the web comic.
4 Respect For Shadow Ring
If there's one thing Flashy Flash rarely gives out its compliments. He's far too full of himself to ever admit someone is at or even near his level. It took multiple occasions before he begrudgingly admitted that Saitama had skill, far surpassing what his rank may say.
Why then does he hand it out to Shadow Ring? Is it because she's a ninja-like he is? It could be the case, as her talents reminding him of his time there. Unfortunately, it's never explained as the two rarely interact.
3 Hatred Of Sweet Mask
While Flashy Flash isn't exactly friendly with any S-class hero, none get on his nerves quite as much as Sweet Mask does. The two have nearly come to blows on some occasions and are more antagonistic to each other than some villains are.
The funny thing is that Flashy dislikes him for being too arrogant, which is a total pot calling the kettle black moment. They are far too similar, but it never makes any sense why so many heroes dislike one another in the series.
2 A Ninja In A Cape
For a character who'd been raised to be a ninja, people known for their stealth prowess, it's dumbfounding that he's always wearing such a flourishing cape. Sure, it can help shield himself from liquids, as it did against the Hundred-Eye Octopus, but it's still too showy and flowy to make sense. It makes even less sense when you consider that he's essentially a speedster. Why would you want a long garment potentially getting in the way of your movements?
1 Inconsistent Powers
Much of this can be chalked up to the difference between the web comic and the manga/anime. His ability range in the web comic is far higher than seen on screen, proving capable of creating literal hurricanes by spinning his sword at high speeds. He can also create after images and several other things yet to be seen beyond the comic. It's a shame because spawning a massive cyclone sounds far cooler than the ultimate technique he has on the show.