I use to shred my paper napkin if I was eating out/with a group. I found it a little funny because I'd really really shred it and not be away and at the end of the meal there'd be this ball of "strings" of bits of napkin, LOL. Everyone including myself would look at it and I'd just shake my head and laugh.

Sometimes I jokingly "warn" people if I know I have an unconscious behavior that looks weird. I'd say something like, "okay, you have to warn me if I'm doing a lot of scratching because I go for the bone without realizing it and if I start bleeding, I'm going to blame you!" Other people are startled but not more so than seeing you bleed and enjoy being of help to you with your unconscious habit.