The Dragon Ball universe is defined, first and foremost, by its heroes. Goku, Vegeta, Gohan, and the rest of the Z-Fighters have all contributed to the series and its history in ways that made for memorable moments. Those moments were memorable all thanks to their bold, daring, and ultimately brave actions in saving lives and beating the bad guys.
However, being the bravest heroes does not exempt the Z-Fighters from also making some of the dumbest decisions. These heroes have not always made the smartest or even the most heroic decisions and some of their worst decisions nearly put the world at risk.
10 Goku Gave Cell A Senzu Bean
Despite being arguably the most powerful fighter in Universe 7, Goku can be a bonehead sometimes. One of his most boneheaded decisions came when he not only tagged out of the Cell Games in favor of making his 11-year old son fight The Big Bad, but he gave said Big Bad a Senzu Bean for the sake of a fair fight.
Gohan was already at a disadvantage in age, size, and power level. His father gave Cell an extra boost, thus widening that gap of disadvantage. It created a domino effect that eventually led to Goku's death. Maybe he'd still be alive if he didn't take such a bold gamble, but either way, the Senzu Bean certainly didn't help matters.
9 Gohan Didn't Finish Cell Off When He Had The Chance
To Goku's credit, his overconfidence that his son would be capable of beating Cell actually paid off when Gohan went Super Saiyan 2. Granted, that saving grace may have never happened if Cell hadn't stomped on Android 16's head, but he did and Gohan made him pay for it. Almost too well.
The power boost gave Gohan the power to end the fight much sooner, but he didn't, instead deciding to relish in beating up Cell without mercy. Unfortunately, that gave Cell plenty of time to spit up Android 18, blow himself up in a wave that killed Goku, and shoot a kill shot in Trunks' direction.
8 Vegeta Willingly Gave In To Evil Again
While not yet having a full-blown redemption arc, Vegeta spent years as an acclimated member of society long before the Buu Saga rolls around. However, all it takes is a return from the afterlife from Goku to convince Vegeta to throw it all away in an attempt to essentially make a deal with The Devil.
He willingly let himself come under Babidi's control to receive the power he needed to finally beat the one Saiyan warrior he failed to defeat years prior. Even worse, he knew the consequences of their fight would revive Majin Buu, the planet's next big threat. Ultimately, it all cost Vegeta his own life in a sacrifice that could've easily been prevented if he wasn't so selfish.
7 Trunks Went Super Saiyan Third Grade
In theory, Trunks had the right idea to ascend to a higher grade of Super Saiyan. After all, this was the closest that the Z-Fighters came to matching Cell in strength, but that's all Trunks did here -- match Cell in pure strength.
He overlooked the fact that turning himself into a huge hulking mass of a man would significantly power down his speed. Trunks quickly learned that being as strong (if not stronger) than his opponent is meaningless if he's too slow to catch up to them or dodge incoming attacks.
6 Piccolo Killed Goku
When they entered their fight with Raditz, Piccolo and Goku were not so much friends as they were temporary allies teaming up with a common goal. Piccolo decided to take out both of his enemies with one fatal Special Beam Cannon.
While Piccolo got his wish, it created a problem when, suddenly, the Earth was without its mightiest hero upon news that even stronger Saiyans were approaching the planet. And when the other Saiyans did arrive, a countless number of people died, including more than half of the Z-Fighters and Piccolo himself. A revived Goku arrived to clean up Vegeta and Nappa, but one has to wonder if there'd be fewer casualties if Piccolo found a solution that didn't kill the Turtle School graduate.
5 Yamcha Cheated On Bulma
Disregarding that their relationship often consisted of on-and-off breakups, Bulma and Yamcha dated each other exclusively for the better part of 15 years between Dragon Ball and Dragon Ball Z's Android Saga. That relationship may have lasted a little longer if Yamcha was not so insistent on flirting and cheating with other women.
In Akira Toriyama's own words per Yamcha's voice actor Tōru Furuya in an interview for the TV Anime Guide Dragon Ball Tenka'ichi Densetsu, "Come on; Yamcha's a cheater." The big lug can't help himself, but if he could, maybe he wouldn't still be attempting to be a womanizing bachelor in his late 40s.
4 Majin Buu Overslept
The baddie-turned-goodie Majin Buu was ready to make good use of his abilities in the Tournament of Power as a representative of Universe 7. However, he overslept with the fate of the universe on the line.
Because Buu couldn't keep his eyes open long enough to spar with the toughest fighters of the multiverse, Goku was forced to venture into Hell to recruit Frieza as a last-minute replacement, which caused its own disastrous repercussions along with the struggles the team had in working with a conniving rival. They also had to keep up a bargain Goku made to officially bring Frieza back to life. Unsurprisingly, Frieza was right back to his own schemes and nearly unleashed an unstable Broly on the entire universe soon after.
3 Krillin Didn't Turn Off Android 18
Krillin had one job. Bulma was able to use schematics originally designed by Doctor Gero to create a Shut Down Remote to literally turn off Android 18 before Cell could absorb her and become Perfect. Krillin just had to get within walking distance of the android and press a button, but because he had a crush on the artificial cyborg, Krillin couldn't do it. In fact, he destroyed the remote, opening the door for Cell to get what he wanted.
Imagine how many deaths could have been prevented if Krillin just did his job. On the plus side, at least he found a wife out of the whole thing.
2 Tien Scammed A Village
It is often forgotten or overlooked that Tien was originally introduced into the Dragon Ball universe as a villain. His first appearance came when Goku met him and Chaiotzu in a village terrorized by the beastly InoShikaCho.
Tien and Chaiotzu killed it and emerged from the affair as heroes, only for Goku to discover that the two didn't kill the beast at all and they were just con artists all working together for the sake of profit from the villagers rewarding them. Even worse, when Goku tried to expose them, Tien tried to flip the tables by claiming it was Goku doing the scamming.
1 Master Roshi Couldn't Control His Perverted Mind
Since his character has always been the living embodiment of the word "pervert," there are several things on his résumé that can be classified as being "the worst," but this one typically sticks out as an early example because it is one of Master Roshi's earliest appearances. What a first impression.
Upon discovering that Master Roshi has a Dragon Ball in his position, Bulma tries to proposition him for it. Of course, Master Roshi's mind was quickly consumed with inappropriate ideas.