DISCO LEG

The shaking or jiggling of a single leg absentmindedly or obsessively when nervous. Usually consists of moving one knee up and down by bouncing the leg on the ball of one foot when in the sitting position. Also descriptive of decrepit or infected livestock. Example: Jethro, I think one of your dairy cows might have BSE (Bovine Spongiform Encephalopathy)-- it's got a clear case of disco leg.