I got the sternum pops (glad to hear I'm not the only one because it really freaked me out the first time I did it), the hip pops, the jaw cracks, and I will, at times, compulsively do the wrist-crack-thing. Oh, and if I'm not wearing shoes I will flex my toes and crack them like there's no tomorrow. Sometimes if they're not cracking to my satisfaction, I'll press my toes down with my hand and pop them way down in the base of the joints.
I don't bite my nails, but I do have a biting problem - especially when I'm stressed, I bite my lips and the insides of my cheeks. I bite that first dead layer of skin any place where it will come off, and, like the people with the war zone nail beds, I'll often start myself bleeding. And I still won't stop. I've tried to go cold turkey since I read that doing it can increase my risk of oral cancer, but I still go back to biting in a few days.
Wow, that sounds a lot more gross written out like that than I thought it would.