At lunch one day last week, I realized that almost all the people around me (all men, Silicon Valley types talking about Silicon Valley matters, so far as I could tell) were jiggling their legs, apparently without any realization they were doing so. I’ve long been familiar with the behavior, though never in such a concentrated form; it was like I had fallen into a convention of leg-jigglers. (I am not one.)
Quite a number of variants: some one-legged (mostly the left, in this small accidental sample), some two-legged; and some subtle, a light bouncing off the ball of the foot, and others more vigorous, up to one guy who was pumping his left leg extravagantly.
Unfortunately, not a whole lot seems to be known about leg-jiggling / leg jiggling, leg shaking, foot jiggling, or sewing-machine leg, as it is variously known.