One of my best friends in the world bounces his leg often. He's a bigger guy and it can definitely get annoying. I try to just let it go unless we're sitting at a table and he's shaking it too, then I will gently reach over and touch his knee to let him know. He immediately apologizes and stops, and I feel bad for having to say something, but I draw the line at shaking the table lol. If he's sitting across the room from me he can bounce to his heart's content.