A little boy is playing with his new football and a little girl asks if she can play. He tells her, "No. These are for boys."
The little girl runs into the house and tells her mother. The next day the girl sticks her tongue out at the boy and waves her new football in his face. The little boy angrily points to his boy's bike and says, "Oh yeah? Well, only boys can get these!"
But the next day, the little girl has the same bike. The little boy gets furious, pulls down his pants, points to his unit, and says, "Look, only boys have these and your mom can't buy you one!"
The next day he walks by and the little girl promptly pulls up her dress, points to her bits, and proclaims, "My mother tells me that as long as I have one of these, I can have as many of those as I want."