Without a bike?
Running from a hill, falling on broken glass resulting in an operation to remove a piece from my knee (they told me I was lucky as I could loose the ability to bend my leg forever). I was about 6 years old and I clearly remembered arguing with my mother that day. She wanted me wear long pants, I insisted on shorts and won.
On a bike - falling at 0 speed on my elbow 30 meters from my house when I almost passed out from pain (hit the nerve ending). I was a lame rider that time.