If I get too excited about something, I lose control of my hands for a short amount of time and end up flailing one of them. It sounds childish, but it's actually subconscious and I have little to no control over it, much to my frustration. It's been the case since I've been a child, and it is awful when in public, because people often notice and say nothing, but give you that look of "..What on Earth..?".