Bob says to his friend Bill, "My doctor says if I don't give up sex, I'll be dead in a week."
"Why is that?" Bill asks.
Bob replies, "I've been screwing his wife."
"I have to be very careful not to get pregnant," a woman told her friend.
"I don't understand," said the friend. "I thought your husband had a vasectomy."
The woman answered, "Precisely."