have you ever seen someone fall on there ass and jump around holding there ass for a fiew minutes. its helarouse.  im not saying this is though, think about how much you use your ass, you sit on it, you sleep on it, you fall on it and you do other stuff.  man that would suck.  x ray would go straight to the balls too.  oh man, i would hate to break that, i have never gotten hurt on a rail, hit my hip once.
~Tom