It's a habit I'm generally very good about controlling, but when I get overly bored, I'll start biting my nails. It's a horrible habit, and it hurts after a while (it's not uncommon to bite and chew till I bleed), but dammit, sometimes you just can't stop. It's like, those little twinges of pain are enthralling. It's not like cutting or just bashing your head against the wall. It's unique, and it leaves you wanting more.
See, but now my fingers hurt, and I regret it. :\