You Don't Have One of THESE

Little Johnny and a little girl are playing. Little Johnny pulls down his shorts and says, "I have one of these and you don't."
The little girl starts crying and crying and runs home to her mother.
The next day Little Johnny and the girl are playing together again. Once again Little Johnny points to his private parts and says, "I have one of these and you don't."
But this time the little girl just keeps on playing.
"How come you're not crying today," asks Little Johnny.
"My mother told me," says the little girl, pulling up her dress, "that with one of these, I can get as many of those as I want."