I like to bite off only part of a nail and then play with the loose end. I leave it like that until I get bored with it and pulpy the rest of or I forget about it and it falls off.
I pace around a lot, helps me think I guess. Whenever I'm having a debate in my head or imagining some situation I end up walking about the room or the house. It's definitely a compulsion, I get very uncomfortable when I don't do it.
I get distracted in my thoughts a lot when reading books which usually results in me walking around my house/room.
Since I don't chew my food very well I end up regurgitating it sometime through the day. When I do I usually leave it on my mouth, chew it up some more, and swallow it again. I also enjoy the taste, which is probably the weirdest part about it.
I'm always having long debates in my head. My inner voice just won't shut up. Oddly enough when I'm high my internal voice completely disappears, which seems to be the opposite effect for what most people experience.
I sometimes act out what I'm daydreaming without thinking then try to pass it off as a scratch/stretch/whatever, my expression changes too but I'm less able to control/hide that.
When I go quiet in a conversation its because I'm following a train of thought and only half-listening, this can last anywhere from a minute to half an hour, I'll then awkwardly raise the topic again and give a lecture about my conclusions/reasoning. After this people who I haven't done this to before tend to assume I've not been listening to them, they make the accusation then I paraphrase back to them what they were talking about and my thoughts on it.
Yeah, I do that a lot too. Especially the first one.