I'll break the chain and say that I actually don't restrict myself. If I feel the need to flap my hand, wiggle my fingers, bounce, etc., I do it. I mean, I don't go all out flailing and jumping; I think it's only something people would notice if they were looking right at me.
For one, I do this because I never found an effective substitute. I tried carrying certain bracelets or objects around with me, but they didn't work. Physical movement just helps me a lot more.
For two, I've never been concerned about how I look in public. I've sported green mohawks, the tackiest of thrift store clothing, gruesome horror movie t-shirts, you name it. Just like with self-stimulatory behavior, that's just who I am and how I express myself, and I don't see a need to repress it just because some stranger on the street might think I'm weird. Of course, that's just my own experience.