A girl calls up her mother and says,

"Ma, I met this Greek guy, and I'm in love with him, and I'm gonna marry him."
Her mother says, "All right. You wanna marry a Greek guy, that's fine with me. But whatever you do, don't let him flip you over."
About six months after they're married, they're lying in bed one night and her husband says, "Honey, why don't you turn over?"
She says, "Oh, no. My mother told me never to turn over."
He says, "What, don't you wanna have any kids?"