What is the stupidest thing to happen for plot convenience?

[Mystic]

The two that immediately spring to mind for me are

2) Vegeta deciding to let Semi Perfect Cell achieve his final form.

1) Goku saying he didn't kill fat Buu because he wanted to make way for the younger generation. It could just have easily been "I might've been able to, but the transformation is too strenuous and I don't think I would have had enough time"

I don't think Gohan missing the potara is as egregious but that's kinda stupid too.

 

[Warmmedown]

Bulma driving a car at 14.
edit: nm, she was 16

 

[Hector]

Piccolo talking to the kids in the spirit room.

 

[Papasmurf]

The androids not just taking the 2 minutes it'd take to fly to Goku's house and kill him when they had the chance because "it was a game."