An old man goes to the doctor. The doctor asks for stool, urine, blood, and semen samples. The old man can't believe it. He takes all his little sample jars and goes home.
At home, he tells his wife that the doctor wants stool, urine, blood, and semen samples.
The wife looks aghast and then realisation spreads like the dawn across her wrinkled facial features. "That's easy," she says, relief obvious in her voice. "All he wants is your pajama pants!"