What's the stupidest thing you've ever done?

I convinced my brother of the merits of drinking a couple of bottles of blue food colouring. He got a very upset about his stained teeth and tongue, but his emotional state deteriorated after spending the next week doing blue poos.

I coerced a mate into carving 666 on his forehead (I was retaliating - won't go into details). There was still visible scarring a year later.

I'm quite fond of the power of suggestion :)

Fucked myself up plenty too, but you lot have covered most of it already.