Constant tapping of a pencil or pen :sweetjesus:
This, except for me it's just fingers. They'll be driving a car, watching an emotionally captivating movie, or desperately trying to think of something to do in general but that won't stop them from drumrolling their fingers constantly.
 
My biggest pet peeve?
Dogs yipping and barking.
I. Fucking. Hate. Dogs.
Cats are better.
 
And also when you're trying to sleep and all you can't because the next door neighbors are hitting the wall and moaning all night long :\