An old man went in to see the doctor and said, "Doc, I'm turning eighty tomorrow and I don't know how many more years I have left. My good wife died ten years ago and I've had no sex at all since then. I'd love to experience sex one more time before I die so I've hired a hooker for the night. Can you give me something that'll help me get it up?"
The doctor smiled. "I don't normally prescribe this stuff as it's extremely potent, but I think in your case I can make an exception for one night."
Later that night, out of curiosity, the doctor phoned the elderly man and asked, "How's it going?"
"Fabulous," the old man said, "I've come three times already."
"That's great," the doctor said. "The hooker must be astounded."
"Not exactly," the old man said. "She's not here yet!"