Another old favourite ....
A man saw an ad in the paper for pills that make you fifty years younger. Since he was approaching middle age, he sent off for some. But before the pills arrived, he went away on holiday.
When he got back after the holiday he was met at the airport by a very attractive young woman with a baby in a buggy.
“Who are you?” he asked.
"I'm your mother,” she replied.
He said, "You can't be my mother, my mother's an old woman."
“I am your mother,” she said. “I took one of those pills you sent away for. You know, the ones that are supposed to make you fifty years younger."
“My God, that’s incredible,” he said. "And who’s this in the baby buggy?"
"Oh, that’s your father. He took two."