Little Johnny (smartass & hero of many jokes) is a little tired of being the only one in his class not to benefit from his teachers kindness.
Every Friday she declares a quiz question, and the first to answer it correctly gets to leave early.
One Friday Johnny goes prepared with two ping-pong balls painted black.
Once the teacher announces that it's time for the weekly quiz Johnny bounces the balls to the front of the room.
"O.k. says the teacher, who's the comedian with the black balls?"

"Sammy Davies Junior, Miss, see you Monday!"