When I was younger, I played soccer. During a game, I decided to be an idiot and kick the ball straight on with my toes instead of the inside of my foot. Needless to say, I'm never doing that again. Due to the somewhat-flimsy-ness of soccer cleats, when I kicked the ball with a forgetton of power, the nail on my big toe was shoved backwards into my toe about 1/16 of an inch. Blood everywhere, couldn't walk properly for like two weeks.
Another really painful moment is when I fell off my bike when I was younger and landed directly on both my hands simultaneously, instantly breaking both wrists. I couldn't get myself up off the ground because every time I tried to push off the ground, it felt like someone was driving really, really long nails up my arms through my wrists.