You Have Mine And I Have Yours
A woman is at home when she hears a knock at the front door. When she opens it there's a man standing there who shouts at her: "Hey lady, do you have a vagina?" Scared, she slams the door shut hoping he'll go away.
The next morning she hears a knock at the door again. It's the same guy and he asks the same question. "Do you have a vagina?" And again she slams the door only this time she calls her husband. The husband tells her he'll take off from work the next day and find out exactly what this guy is up to.
So the next morning, with the husband hiding behind the door, here comes that knock again. The husband signals to his wife she should answer yes this time. When she opens the door and the guy asks, "Do you have a vagina?" the wife says, "Yes I do."
"Perfect" the man replies, "Tell your husband to leave my wife's alone and start using yours!"