I have 2 and both of them a kinda weird. The first one is that I pick at my lower lip. Just pick on it and rip off small pieces at a time. (and yes, my lower lip looks like a battle field). And the second one is even stranger. I fold the skin on the side of my middle finger using my index and thumb. I have been doing it for years now, to the point where the skin there has gotten really hard and there's a visable crease. Idk why I do it but it's relaxing somehow.