A little boy about 12 years old is walking down the street dragging a flattened frog on a string behind him. He came up to the doorstep of 'a house of ill repute' and knocked on the door.
When the Madam answered it, she saw the little boy and asked what he wanted.
He said, 'I want to have sex with one of the women inside. I have the money to buy it, and I'm not leaving until I get it.
The Madam figured, why not, so she told him to come in. Once in, she told him to pick any of the girls he liked. He asked, 'Do any of the girls have any diseases?'
Of course the Madam said 'No'.
The boy said, 'I heard all the men talking about having to get shots after making love with Amber - THAT'S the girl I want.'
Since the little boy was so adamant and had the money to pay for it, the Madam told him to go to the first room on the right.
He headed down the hall dragging the squashed frog behind him. Ten minutes later he came back, still dragging the frog, paid the Madam, and headed out the door.
The Madam stopped him and asked, 'Why did you pick the only girl in the place with a disease, instead of one of the others?'
He said, 'Well, if you must know, tonight when I get home, my parents are going out to a restaurant to eat, leaving me at home with a baby-sitter. After they leave, my baby-sitter will have sex with me because she just happens to be very fond of cute little boys. She will then get the disease that I just caught. When Mum and Dad get back, Dad will take the baby-sitter home. On the way, he'll give her one in the car and he'll catch the disease.
Then when Dad gets home from the baby-sitter's, he and Mum will go to bed and have sex, and Mum will catch it.
In the morning when Dad goes to work, the Milkman will deliver the milk, have a quickie with Mum and catch the disease, and HE'S the prick who ran over my FROG!'