That's an old one but still cute. Have you seen the one, it's actually old too, but a husband wants to have sex with his wife and she tells him "no" because she has to go to the gynecologist the next day and she wants to be "fresh" and then he asks her, "do you have a dentist appointment too?"

__________________
The woods are lovely, dark, and deep, but I have promises to keep and miles to go before I sleep...