The little girl asked her school boyfriend what a perfect penis was.
He confessed he didn't know, but would ask his Dad and let her know tomorrow.
Upon getting home he put the question to his father, who, not knowing how to answer, decided to demonstrate by dropping his trousers and boasting "This is a penis my son, and it happens to be perfect"
The following day the little girl asked her boyfriend if he had managed to find out for her. Taking a cue from his fathers demonstration, he dropped his pants and explained "This is a penis - and it would be perfect if it was smaller".