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bitter smile; wry smile; forced smile; strained laugh
失敗を指摘されて苦笑いした。
I gave a wry smile when my mistake was pointed out.
彼の苦笑いが印象に残った。
His bitter smile left an impression.
苦笑いを浮かべながらも引き受けてくれた。
He accepted it with a forced smile.