a joke from my boy scout days, 7 years ago:
Warning: Contains implications of corporeal punishment and/or child abuse
One evening, a father went up to his two sons. "All right, who pushed the outhouse into the lake?"
Both sons immediately denied it.
"Boys, let me tell you a story," said the father. "When George Washington was just a young boy, he cut down his father's favorite cherry tree with a hatchet. His father demanded to know who cut down the cherry tree. 'Father, I cannot tell a lie,' said young George. 'It was I who cut down your cherry tree.' And his father was so impressed by his honesty that he decided not to punish George."
The two sons looked at each other. "Father, I cannot tell a lie," said the older son. He pointed at his brother. "It was this guy! It was all him!"
Disappointed and hurt, the father sent the older son to his room without dinner.
Later that night, the younger son came up to his father. "Father, I cannot tell a lie," said the younger son. "It was me! I'm the one who pushed the outhouse into the lake!"
"Why, you little brat!" shouted the father, removing his belt to strike his son.
"Wait!" protested the younger son, panicking. "You said George Washington's father was so impressed by George's honesty that he didn't punish--"
"George Washington's father wasn't in the cherry tree when George cut it down!" shouted the father, chasing his son out of the room.