I've been stuck to a tree by my hair while 3 people shot at me. Not damaging, but painful.
Worst injury I've ever seen was at a FR game last year where my friend tripped in a ditch and tore the ligaments in his leg. He still cant attend games.
A nail through the foot came second. Although, that doesnt stop airsofters. Once some gauss and duct tape was located the guy came back into the game, hopping around with a mac11 on his good foot.
Before the internet, the village idiot would stay in his own village.