Hurt.
Said bad words. A lot of them.A friend of mine who's a professional contractor shot himself through the kneecap with one.
No finger on the trigger in his case. It was defective. As soon as it hit something it would fire, without the trigger being pulled. He knew this. In fact, he wouldn't let any of his guys use it because he was afraid they'd hurt themselves with it so he used it himself. Was trying to pull some slack in the air hose and it bumped against his knee and BLAM.