I've done a bunch of martial arts, gotten into fights, fell 20 feet out of a tree (saved by branches and a rotten log, woo), got accidentally slashed with a knife and could see the inside of my hand, been hit with a wooden baseball bat, skateboarded (and fucked up plenty of times), mountain biked (and fucked up plenty of times), and been attacked by a dog but I'd have to say, hands down, car wreck.
Wasn't even that bad an accident, but I was bruised all over, sore as shit, and had a concussion.
Shit sucked and it could've been a lot worse, I was pretty lucky: Be careful when you're driving, always pay attention, and assume everyone else is a dangerous idiot. Also, wear your fucking seatbelt!