Ah, one of my many addictions...among things like candy
, married rockstars, and Everything2
Anyway, for most of us nail-biters, we don't do it because we're stressed or nervous, even though it increases when we are. We do it just because it's a nasty nasty habit.
It's more than a "thing to do with your hands". I sit here typing now, finding my hand going to my lips and then using it to hit myself in the face because YOU SHOULDN'T BITE YOUR NAILS! Everytime I find myself doing this when I'm not doing something else with my hands, i.e. eating or playing an instrument, I just sit on my hands. For real. Do it. I mean, no one's looking. Don't do this in public. Or, if that's just too weird, hold someone's hand.
Anyway, something else you can do is put something nasty tasting on your fingers. I'd say vinegar, but that smells pretty awful. Perfume also tastes bad, so just try that.
It also helped me when I asked my friends to inform me when I'm biting my nails. Ask a few close friends (because it'll seem weird to others) that you hang with a lot to tell you when you're chompin' and to tell you to stop. Or kick you, whatever works for you.