the Plano Clap is a motion of tapping your fingers on the inside of your arm, inferring the use of heroine. It is a derogatory stereotype commonly used against youth from the North Texas area against residents of Plano. It suggests that all actions from the people in Plano are based souly on their drug use, particularly heroine and implies an undertone of stupidity.
person 1: Did you see Blake at the party? What a fucking idiot. They were all over the place. Obviously on something.
person 2: Oh definiately. That's Plano for ya! Do the plano clap!!