A twelve year old boy walks into a bordello dragging a dead frog on the end of a rope. He slaps a hundred dollar note on the counter and says to the madam, "I want to see a prostitute." The madam says, "Eh, you're a bit young for this. Why don't you come back in a few years time?" The kid slaps another hundred on the counter and says, "I want to see a prostitute tonight." The madam says, "Okay, take a seat. That'll be about an half hour wait." The kid slaps another hundred on the counter and says, "I want to see a prostitute with active syphillis." The madam says, "That'll be about a five minute wait."
So, after five minutes, a prostitute comes down the stairs and collects the twelve year old boy, who follows her upstairs again, still dragging this dead frog on the end of a rope.
After a little while he comes back down the stairs, having done the deed, still dragging this dead frog on the end of a rope.
The madam says to him, "Tell me – why did you want to see a prostitute with active syphillis?"
The kid says, "Well, when I get home I'm gonna sleep with the babysitter. And after mum and dad get home, dad will drive the babysitter home, and he'll have sex with her on the way. Then when dad gets home, he'll have sex with mum and in the morning after dad goes to work, mum will have sex with the milkman, and HE'S THE BASTARD WHO RAN OVER MY BLOODY FROG.