Ergh. I never really got over the scene in House of Wax where that guy gets his tendon severed. But that only horrified me because I know that it can actually happen under normal circumstances, and that it would be bloody painful (as well as just plain bloody).
When I read Harry Potter and The Half-Blood Prince, I was equally disgusted at the beginning where Malfoy stomps on Harry's face and breaks his nose. Just thinking about it makes me cringe - I mean, I bashed my nose on the door by accident and that was painful. So I guess I'm only disturbed by things I can empathize with. Films with zombies and murderers with amazing abilities don't really scare me, because my Ti slaps my Ne in the face before it can speak up, saying over and over again: "Well that can't possibly happen because... No, shut your mouth, it can't possibly happen. Moron."
But realistic injuries that could happen IRL? They get to me.