A third grade teacher told her class, "Children, we are going to begin to study a little sex education. Tonight, girls, your first assignment will be to find out from your parents how to avoid getting pregnant. For you boys, your assignment will be to go home and find out what a penis is."
So little Johnny goes home and asks his father, "Daddy, what is a penis?"
The father pulls down his pants and points proudly saying, "Son, that is a perfect penis."
The next day, when Johnny gets to school, his best friend runs up to him on the playground and says to Johnny, "I forgot to find out what a penis is! What's a penis!"
Johnny tells him, "Come on." So they both go into the boys room and Johnny pulls down his pants. He points down and says, "There, if that was a little smaller, it would be a perfect penis!"