With thanks to Paladin, who emailed me the following:
An old timer goes to see the doc because he's having "trouble" in the romance department.
The doc gives him a prescription for some Viagra and tells him to come back in 3 weeks.
Three weeks later, the dude comes back, and the doc asks him, "Well, how's it workin' for ya?"
"Good, good," says the dude.
The doc says, "Your wife must be really pleased, huh?"
"I don't know," replies the dude. "I haven't been home in 3 weeks!
Mrs. AOW didn't find this joke so damn funny.