I have a habit of whacking my teeth together in my sleep, or perhaps as I'm just coming out of it. It's not a natural open/close motion either, it's like the top part of my jaw is offset sideways so the front of my teeth on one row hit the back of another. One of these days I'm going to end up doing some real damage.
Back to the original prob, I knew a guy in high school who cut off a part of his tongue for a dare.
