My oldest son has a horrible habit. He bites his nails -- all of them. Even his toenails! Tonight I walked into his room to put him to bed after giving him some time to read, and found that he had his foot in his mouth! He looked at me, and knew immediately that he was in trouble. It's just horrifying to find him munching on something and then to ask him what it is, only to have him roll his eyes with guilt and admit that it's a finger- or toenail. Ewww.
He's always had some kind of bad habit, though, as long as I can remember. It started with his drooling as a baby -- but who can blame him for that?! Except, he didn't just drool, he drooled. The kid produced so much fluid that he literally would stain his clothes yellow. I'm not even sure where all that fluid came from -- especially since my wife nursed him for a good long time, and she wasn't exactly a shriveled up prune. It was amazing.
Then he moved into his picking-the-lip phase. This was simply awful, as he would cause his own lips to bleed by picking at them so much. He'd stop doing it long enough for his lip to scab over and heal a little bit, but then he'd start right back up again.
Then he moved into the picking-his-nose stage. He still does that fairly regularly, but lately it seems he only does it when he's bored in church as we're sitting near the front where everybody can see him. I swear, everybody's going to know him as "that boy that picks his nose". He also has a tendency to do it while watching TV. It's absolutely aggravating because he doesn't even have anything in his nose to be picking at!
And now we've got the picking/biting-of-the-nails habit. His teacher apparently hasn't really noticed it in class, probably because she keeps him so busy. At home, however, we find he does it pretty much any time he's reading a book. Occasionally he'll do it at tennis lessons when he's not paying attention. We also notice it when he's nervous about being in a new learning environment.
His nails are always bit/picked down to the skin, and even so, he still finds nail at which to pick or bite. There was a time we would have him wear gloves to school -- didn't work. We'd have him wear socks all the time -- didn't work. We tried the nasty tasting nail polish -- it still doesn't work (which is probably how he added the picking part to the biting). It's a miracle he doesn't cause his fingers to bleed. We've even tried bribing him -- offering him a toy of his choosing should he break the habit long enough for us to need to cut his nails. No go. We literally haven't had to cut his nails in several years.
As a young child, I learned to crack my knuckles. It was the cool thing to do that my parents hated, and I still do it on occasion to this day. (To relieve tension! Really!) Perhaps this is just payback, and I should be grateful he doesn't have nervous twitches, outbursts of cursing, or severe flatulence problems.
I just hope he learns to control this habit one day, but if not, I suppose there are worse habits to have.