Standing at the edge of the lake, a man saw a woman flailing about in the deep water. Unable to swim, the man screamed for help. A trout fisherman ran up.
The man said, "My wife is drowning and I can't swim. Please save her. I'll give you a hundred dollars." The fisherman dove into the water. In ten powerful strokes, he reached the woman, put his arm around her, and swam back to shore.
Depositing her at the feet of the man, the fisherman said, "Okay, where's my hundred dollars?"
The man said, "Look, when I saw her going down for the third time, I thought it was my wife. But this is my mother-in-law."
The fisherman reached into his pocket and said, "Just my luck. How much do I owe you?"