When I used to race years ago - athletics (100m) - I used to throw up before races
That's partly why I stopped doing it.. I'd spend half a day feeling awful just for 11 seconds of racing...
Other than that my knee shakes if I'm sitting down and being nervous, particularly if I'm tired anyway. I found that out recently
And I once knew a guy who had to manically tear the labels off his beer bottles if he was talking to a girl in a bar.. He'd tear them into little pieces without realising it and leave little shreds everywhere where he'd been sitting