I'm a member of the cracking things club. I can crack literally every joint if they sit awhile this includes every knuckle on my hands. The knuckles on my right hand, wrist, elbow, and shoulder all crack at will continuously. My neck, left hip, and right ankle also crack at will. It's like I'm slowly falling apart or something.

^ I too experience the random cracking of various body parts, mostly in the elbow, knee, and toe regions. I used to crack my knuckles till I started worrying about my joints as I grow older. I don't wanna be decrepit!
Other habits include former nail-peeling (no cutting, just peeling. I pulled off a chunk of nail on my toe once, learned from that.), scalp scratching (to the extreme, wherein I'll occasionally open up a hole, though I've been doing it less, recently). Swearing was a big one back in high school, but I've tamed my tongue. It's more civilized and refined now (with some help from university philosophy :p).

I've got some nose picking going on... I've gotten subtle about it though...

I put random things I find into my pockets. I stick random things I find in my pocket into my mouth. >.>

Also, I sometimes decide that this old scar on my leg itches really really bad, and scratch it 'till it bleeds. There's also that poking and prodding of bruises others have mentioned, and I chew on pencils.

I don't know why, but I have trouble understanding when people speak to me. Sometimes I don't feel like bothering with it, so I just pretend like I do and nod my head...ussually I decide to do this right when they're saying something important.

Thats not a bad habit... thats Cleptomania

Not so much if it belongs to you, you know.

I heard that it's okay to crack joints, and it does no lasting damage. What are the thoughts on that anyway? Is knuckle-cracking really that bad?

As far as I know cracking your knuckles doesn't do any damage. It is, however, a sign that you'll probably get some joint problem in later life because the cracking noises are made be you popping air bubbles in the synovial fluid, which shouldn't be there.

I'm just really fuckin' lazy.

And I never call people back because I hate phones.

I lick my lips TOO MUCH, like every 5 seconds. Knuckle-cracking too.

I lose pens and pencils. Lots.

During school, I'll go though, about, 5 a week. I just can't remember where I put them.

Also, forgetting homework. I hate homework.

Other than that, about everything mentioned here. And, this being summer, I'm in the habit of staying awake until after midnight and waking up after noon.