This man got his prescription for Viagra, and goes home to get ready for when his wife gets home.
He calls her on the phone, and says, "I'll be home in an hour."
"Perfect", she replies. The man thinks her agreement is because the Doctor told him to take his Viagra an hour before. He takes the Viagra and waits.
An hour goes by, the man is ready to go, but his wife isn't home yet. He calls her on the phone and she says, "Traffic is terrible. I won't be there for about
an hour and a half." The man, frustrated, calls his Doctor for advice.
"What should I do?" he asks. The Doctor replied, "It would be a shame to waste it. Do you have a housekeeper around?"
"Yes" the man replied.
"Well, maybe you can occupy yourself with her instead?" said the Doctor.
The man then replied with dismay, "But I don't need Viagra with the housekeeper..."