lottery
A "Lottery tickets have a probability of 1/2 because you have two choices: you either win or you don't. If you buy two tickets, you're sure to win!"
B "You have two choices: you die tomorrow or you don't die, so the probability is 1/2, and you won't receive your lottery winnings because you'll be dead for sure in two days."
It's neatly in the mold of a boomerang joke, using the logic used by the opponent to deny the opponent's claims.
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