Little Johnny kept disrupting his third grade class by regularly letting loud farts.
His teacher kept him after school. When she insisted on knowing why he exhibited such offensive behavior, Little Johnny said, "I do it because I can do it better than anybody, and I'm very proud of that fact."
The teacher says, "If I show you I can do it better than you, will you stop?"
Little Johnny agreed and the teacher placed two pieces of paper on the floor with identical piles of chalk dust on each one. Johnny dropped his pants, squatted down, farted and blew all but a tiny little speck of dust off the paper.
The teacher dropped her panties, lifted her skirt, squatted down and farted, but when she was done there was not a trace of chalk dust left on the paper. Johnny was astonished and asked if he could see her do it again. She was willing and as she repeated the process, Johnny peeked up underneath her skirt.
"No wonder you won!" he exclaimed indignantly, "You've got a Double-Barrel!"