Learning Something Useful

One day, when Billy came home from school, his mom asked him how his day went. He said, "We're learning about sexual education." She smiled, and said, "At least he's learning something usefull." Billy went up to his room. A little later, Billy's mom went up to his room to call him down to dinner. She opens his door and sees him jerking off. She says, "Billy, when you're done with your homework, supper's on the table."