I know there’s only so many poll options, but there are a lot of other bad decisions that come to mind…
Yamcha: Letting his guard down after he beat up the first Saibaman. I get that he was stepping up because he didn’t want Krillin to risk dying a second time, but Yamcha REALLY should not have taken his eyes off the opponent to brag about how he could take on all the Saibamen himself.
Frieza: Ignoring Goku’s warning to stay down while his destructo discs were still active. Honorable mention: trying to kill Goku RIGHT AFTER Goku spared his life.
Goku: trusting Gotenks (who doesn’t take ANYTHING seriously) with the fate of the world during the Majin Buu saga instead of going Super Saiyan 3 and ending things while he had the chance.
Honorable mentions:
Goku: Trying to bumrush Demon King Piccolo with no strategy after Krillin died. This ultimately worked out since he met Yajirobe and Korin after this (senzu beans). Still… this move nearly got Goku killed.
Vegeta: not caring at all when Dr. Gero tried to off his wife and infant son. It really puts into perspective why Trunks went back in time to ask Goku for help instead of his own father.
Bulma: not telling 16 that she removed his bomb. This could have prevented 16’s death.
Gohan: not killing Cell when he had the chance. This one speaks for itself.