expression, noun
waiting to see opponent's move in rock-paper-scissors; playing a waiting game
Literally 'delayed-throw rock-paper-scissors'; cheating by throwing after seeing the opponent's hand. Figuratively, waiting to act until the other side's move is clear, often in negotiations or strategy.
後出しジャンケンはずるいよ。
Waiting to see my move in rock-paper-scissors is cheating.
交渉で後出しジャンケンをするのはフェアじゃない。
Playing a waiting game in negotiations isn't fair.
後出し alone means 'delayed throw' or 'waiting to see the opponent's move', often used in the same figurative sense. 後出しジャンケン specifies the rock-paper-scissors context.
じゃんけん is the standard word for rock-paper-scissors. 後出しジャンケン is a compound describing a cheating tactic within that game.
Compound of 後出し (あとだし, 'delayed throw') and ジャンケン ('rock-paper-scissors'). The exact origin is uncertain, but it likely emerged as a colloquial term for the cheating tactic.