Heh, a few things come to mind:
When I was a little kid, I tried to open the door while standing on a wobbly chair. Door opened, chair fell, I fell on our dog, dog bit me in the face. I still have two little bite marks...
I once cut the cord of a lamp, still in the socket. Bam. You'd think I'd learn something from that. I didn't. A few years later I tied some copper thread around a piece of wood, and into the socket. Guess how that ended.
I barely ever go skating, and our P.E. teacher thought it was a good idea to go roller-skating. I rolled for about one meter, and fell on my backside. It hurt so much, I had to laugh. Yeah, call me weird.
This one happened to a friend of mine: He broke his little toe because of a very dangerous game. Monopoly. He was walking down the hall, hit the box, which stuck a bit out from the shelf, and SNAP! He never trusted the game anyway, he always lost...
My school used to have 'Workshop Wednesdays', when the workshop was opened till 10 o'clock or something. they stopped that after some people started coming there drunk. One was working at an electrical saw, and suddenly walked to a teacher. "Sir, I think I cut my finger." "Cut your finger?! You've almost sawn your thumb off!" No, really, he almost did.