This may not be one of those theories that holds a lot of water scientifically, but it seems to me like everyone has to have one bad nervous habit. So here’s where I need the collective help of the SDMB. There are some bad habits (e.g., chewing your hair or your clothes) that are completely unacceptable and revolting, but there must be some habits that tend toward the benign. If anybody can offer anything in the latter category that I can steer my daughter to, I’d be endlessly grateful. Currently she’s cracking her knuckles, which I don’t mind so much myself, but it drives my wife crazy.
So…many…inappropriate…comments…
LOL…yeah, but its his daughter so lets be nice. 
Hmm…not a fan of knuckle cracking, eh? As an avid knuckle cracker I can attest that it is one hard habit to quit. If you’re upset about her getting joint problems though you may not need to worry about that so much. I dislocated a thumb once and went to the “finger doctor” to get it fixed. I had heard that cracking your knuckles can lead to arthritis so I asked him. The doctor did not think that cracking your knuckles will cause any problems…he describes it as a release of built up trapped gas in the knuckle. Maybe someone else has more info on this but that’s what I was told anyway.
If she’s cracking her knuckles I must ask…does she chew her fingernails or cuticles as well? I ask because I also do both. Gross habit and probably bad on several levels but its compulsive and hard to stop. If she is of the nail chewing/knuckle cracking breed its going to be a long battle to get her to change behaviors.
How about doodling? Very addictive, but makes a nice outlet for creativity, and may actually improve drawing skills.
Personally, I like clicking pens. You know, get one of the click-y types of pens and then just sit there clicking it all day. Drives my coworkers nuts, but I enjoy it. 
Leg jiggling reportedly burns calories, but she’d have to restrict to to when she was more or less alone.
When I was trying to quit biting my nails in high school, I would up finger-tapping instead. Not drumming on tables and such, but tapping each finger against the thumb in succession, back and forth. Harmless and just difficult enough to refocus the attention from biting.
It looks kind of weird, though, and my mom said it made me look crazy, so you may want to put that one in the “maybe” category.
That’s one of my favorites. I also crack my toes and my neck (but never my knuckles).
I also used to like playing with Silly Putty, just as a way to get extra energy out of my hands and to strengthen fingers (I started playing with Silly Putty around the same time I started rock climbing). That one’s a little iffy, though, because everyone who sees the Silly Putty wants to play with it, and it eventually gets full of hair and dust and starts to break down into a gross, sticky mess.
Spitting?
My son is 11. For a few months when he was 9, he was into spitting. I explained that it turned my stomach, and he tried to curb it. He is into girls now and the habit is gone.
I misread that in the most horrible way possible.
For the sake of civility and not getting thrown out of class, fidgets should be silent. Ear wiggling works. Nose twitching comes in three categories. You can go lengthwise, like a rabbit, side-to-side, like Elizabeth Montgomery, or you can flare your nostrils. Some folks see nostril flaring as a sign of arousal, though, so be careful with that one.
Is playing with her hair too cutsy?
Chewing pens has a nerdy sort of charm.
And that someone is…Cecil!
Surely tuneful whistling is both harmless and free.
Clean freak.
Hey, at least you won’t have to make her do chores.
And here I thought that this thread was going to be about spiking lonely guys’ drinks in bars, or something nasty like that.
Harmless annoying habits, not bad habits? I vote for ‘twiddling the nap on the sweater’.
That being said, I have no idea how to steer someone else from one habit to another. I used to bite my nails, but then I stopped for a long time. Why? I don’t know. I twiddled my hair on occaision. Then I stopped. No idea why. (It was only later that I cut my hair off…)
Bubble Gum? Saying “like”? Crossing her eyes? Drum solos with pens on desktop?
Rings. Rings rings rings.
I wear rings. I play with them constantly (even in my sleep, my husband has told me!) One or more on each hand, and she can use her thumbs to twirl them around the finger, or slide it up or flip it from finger to finger. It can be done fairly subtly, and rings are something people expect to see on a woman’s hands, so they are never really inappropriate. You can take them anywhere and look good, AND have your bad habit with you at all times. The biggest risk, though, is dropping the rings and having to scramble to pick them up again. You learn when to stop flipping and sliding and when to simply twirl! hehehe
My manager chews her hair. Strange habit, and it really doesn’t help raise my already low level of confidence in her when I see her chomping away during performance assessments, group meetings, and once, in front of clients! She starts eating her hair when avoiding eye contact just isn’t good enough. You don’t want your daughter to come across the way my manager does, so choose a GOOD bad habit for her!
Hmm, I was going to suggest either ring twisting or hair twirling, but I see that I’ve been beaten to them.
I actually suggest that she adopts both. Ring twisting is unobtrusive enough to engage in almost anywhere, and hair twirling can appear flirty, which is a useful little twitch in some situations.
Maybe wait a few years to start her on the hair twirling.
I like the ring-twirling suggestion. Oddly enough, I find myself doing that – right now, in fact. Pavlovian, it is. Hair twiddling, no go – some family history there, unfortunately.