Two neighbors, John and Sam, are always competing.
One day John looks over the fence and spies Sam's wife, naked, watering the garden. When Sam gets home from work, John brags to him that he's seen his wife naked.
Sam wants revenge, so that night creeps over to John's yard and catches sight of John's wife performing oral sex.
The next day, Sam approaches John at the mailbox. "Hey, I saw your wife performing oral sex on you last night."
"Ha ha, the joke's on you," John says, "I wasn't home last night!"