The act of farting in someone's drink. Usually wait for a friend to get up and go to the bathroom, leaving their drink at the bar for an assortment of pranks. It's pretty simple, just wait for them to leave and fart in their drink. It's called pulling an Uncle Bobby, because it's such an asshole thing to do.
Jerry's going potty. Quick, somebody hand me his drink, I'm going to pull an Uncle Bobby and I've got a nice hot eggy one.