lol I do the same thing as ilc. I always have the double bass and everything going, sometimes even with my mp3 player on, so I don't know how loud I am. Until someone stares at me, then I stop.
And then as soon as they look away, I start up again.
lol, I even got yelled at by a teacher once because I was doing that while he was trying to talk to the class.
I just can't help it. Even when I'm not drumming with my feet or hands, I'll tap a beat on the desk with my fingers.