Stupidity: When Christine is told that to remove the curse, all she had to do was give an envelope with the button inside to somebody else and that individual would go to hell. She decides to go to the cemetery where Ganush is buried and places an envelope into her mouth. Had Christine actually bothered to check inside the envelope first to see if the button was inside, she would never have gone to hell.
Stupidity: The characters wish for the resurrection of just one person (Roshi) rather than everyone killed by Piccolo as would be natural (and as they do in anime and manga). Okay, Piccolo in this movie sucks at killing and resurrecting Muten covers 50% of the total body count, but they can't know that.
Stupidity: The type of steak that Clyde demands has a sharp kind of bone inside that can easily be used as a weapon. No prison would be foolish enough to overlook this fact, especially as the warden had everything double-checked.
Stupidity: Having become the leader of the universe's most stealthy fighters, he promptly leads them in a Custer-esque noisy frontal charge into a force with known weapon and technology superiority. Zero effort to utilize ANY of their amazing stealth, just have them slaughtered so badly that the planet has to sacrifice animals to save them from extinction.