Guy visits the doctor and tells him, "Doc, I've got a sex problem. I can't get it up for my wife anymore." The doctor tells him, "Bring her back with you tomorrow and let me see what I can do."
The next day, the guy comes back with his wife. The doctor tells her, "Please take off all of your clothes and lie down on the table." After she's lying there naked, the doctor walks around the table a few times, looking her up and down and all around.
Finally he pulls the guy aside and assures him, "You're fine. She don't give me a hard-on, either."