An older Jewish man married a younger woman. After several months, the young woman complained that she had never climaxed during sex and by birthright, all Jewish women are entitled to at least one climax during sex.
So they went to see the rabbi. The rabbi tells them to get a strong, virile young man to wave a towel over them while they are having sex. This, the rabbi says, will cause the woman to climax, so the couple tries it. After several attempts, still no climax.
They go back to the rabbi. The rabbi says for the bride to change partners and have the virile young man have sex with her and have the husband wave the towel. They try it that night and the young woman goes into wild, screaming earsplitting climaxes, one after the other.
When it is over, the husband smugly looks down at the young man and says, "You see, schmuck, THAT's how you wave a towel!"