Recently, I've been thinking about the dumbest moment in all of DragonBall Z. There are a lot of stupid moments in the series, but this one takes the cake.
At the start of Season 4, our heroes meet Future Trunks. He says that, three years in the future, two androids will appear and take over the world. To make matters worse, the leader of the Z Fighters, Goku, is going to die from a heart virus.
Trunks gives Goku a vaccine, to prevent him from getting the heart disease.
Here's the stupid part: Goku never actually takes the vaccine. I'm serious. A guy from the future literally hands Goku the cure to his disease, and Goku decides not to take it. Twelve episodes later, Goku collapses from the heart disease in the middle of a big battle. Now our heroes have to fight the battle without their leader! Oh no!
Seriously, Goku? That was a dumb move. The next time someone builds a time machine, just to save your life, you should actually pay attention.