I suppose my bad habit is that I constantly chew my fingernails down so far that they hurt, mainly because I'm nervous for an exam, or an atheletic event.
1)Like a lot of people have said, cracking your fingers. Like Adam (fst6) has said, it's a myth that it causes problems in your fingers. I find that if you've started, it's worse to stop than to keep doing it.
2)I tap my fingers a lot when I'm not doing anything. My parents call it "nervous energy." O_o
I chew my fingernails... suck on the end of pencils (I fell once and had to spit it out really fast), I tap my fingers a bit, I do the same thing when I'm nervous, embarrassed or excited so I'm a bit easy to read...
I lack stealth. I am too loud. I am naturally noisier and louder than everyone else. Even when I move, it is apparent that I am present. Good for singing and shouting but horrible if I attempt to hide.
i bite my fingernails, and play my instrument slightly too the side of my mouth. the fingernails thing isn't bad at all. in fact, i do it mostly because i want to. i'm not an extreme biter, i just always keep them at a healthy length. lol. form darck