A little boy about 12 years old walked down the sidewalk 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 came to answer it, she saw the little boy and asked what he wanted.
He said he wanted to have sex with one of the women inside, had the money to buy it, and wasn't leaving until he got it.
The madam figured why not, so she told him to come in. Once he got in, she told him to pick any of the girls he liked.
He asked her if any of the girls had any diseases, and of course the madam said no. But he said he'd heard that all the men were talking about having to go to the hospital and get shots after making love with Mable, and THAT was the girl he wanted.
Since the little boy was so adamant and had the money to pay for it, the madam told him to go upstairs to the first room on the right. So he headed down the hall dragging the squashed frog behind him.
Ten minutes later he came back down, still dragging the frog, paid the madam, and headed toward the door, at which time the madam stopped him and asked him just why he picked the only girl she had 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. When they leave, I'm going to have sex with my baby-sitter, who happens to be very fond of cute little boys, and then she will get the disease that I just caught.
When mom and dad get back, dad will take the baby-sitter home, and on the way, he'll jump the baby-sitter's bones, and he'll catch the disease.
Then when dad gets home from the baby-sitter's, he and mom will go to bed and they'll have sex, and mom will catch it.
In the morning when dad goes to work, the milkman will deliver the milk, and he'll have a quickie with mom, and he'll catch it, and HE'S the son-of-a-b**ch who ran over my frog!!"