"Whoever can answer this next question correctly can go home for the day." Naturally the entire class sits up and pays attention at the possibility of skipping the whole day, particularly the class nerd.
She slams her hand on the desk for emphasis and says, "How many drops of water are there in the ocean?"
Naturally, none of the kids have the answer to such an abstract question. The teacher smugly tells them, "I guess we're all staying, then!"
The next day, the teacher makes the same offer. "Whoever can answer this next question correctly can go home for the day." She slams her hand on her desk for emphasis and asks, "How many grains of sand are there in the desert?"
Naturally, nobody can answer, and the teacher smugly tells them that everybody will be staying. The class nerd decides he's had enough.
At the end of the day, he gets a fistful of ping-pong balls from the gym, paints them black, and wedges them under the edge of the teacher's desk so no one will be able to see them.
The next day, the teacher makes her announcement as usual. "Whoever can answer this next question can go home for the day!" And as she slams her hand on the desk, the ping-pong balls are shaken loose and bounce all over the room to the delight of the entire class.
Infuriated, the teacher demands, "All right, who's the comedian with the black balls?!"
"Eddie Murphy," says the nerd. "See ya Monday, bitch."
