Okay, I'll elaborate on mine now.

I was playing rocket ship on the swingset in third grade. For those of you who aren't me and don't know, rocketship is played by running as hard as you can at the swing (one of those with the curvy rubber bottom, not the hard flat bottom) leaping into the swing horizontally, landing on your belly and flying to the moon.

Anyway, I was a pro at this. The trick to going really high was to get slightly more of my weight in the direction my head was pointing. But one time, I overbalanced.

I flipped out of the swing while it was in mid-air, and landed on my face. It was HORRIBLE, half of my head was covered in mud and I screamed and screamed and my nose bled. And my two best friends took me into the bathroom and cleaned me up and I love them forever for it.