I just nicked this off another site:
A man walked into his doctors office, and asked him for 3 viagra pills.
The doctor asked, "Why only 3?"
The man said, "Well, Friday my secretary is coming over, Saturday my girlfriend is coming over, and Sunday my wife is coming home from her vacation.
The doc said, "Thats more than I wanted to know, but here's your 3 pills."
A week later the doctor saw the man at the gas station, his arm in a cast, and sling.
The doctor said, "What happened to you? Did the women all find out about one another?"
The man said, "No, Nobody showed up....."