Just one of a list of completely idiotic things I've done:
When I was 12 I was biking down the road on a hill outside my house, feet off the pedals, easily travelling 20mph+. Having a jolly good time at it too.
Anyway, the end of the road was coming up at a worrying rate so I thought "Hey, I'd better get this shit back in control."
Oddly enough, when travelling at speed, the motion of the wheels can cause the pedals to rotate themselves; so, as I went to put my feet back on said pedals, the non-slip studs dug into my heels and banged my head firmly against the handlebars.
Naturally I slammed the brakes on, the front brakes. An eye-witness account from my brother goes like this:
"Holy shit, you went right over the handlebars and landed on your face about 15 feet away. Then the bike (which was airborne at the time) landed on your head!"
I can believe that.
Strangely enough, I didn't break or fracture anything.
Made a neat stain on the road though.