sour grapes; the unwillingness to admit defeat; remarks or behavior that deny or excuse losing.
試合に負けた後の発言がただの負け惜しみに聞こえた。
His comments after losing the match just sounded like sour grapes.
負け惜しみを言わずに、相手を素直に褒めたらどうだろう。
Why not praise the opponent honestly instead of making excuses for losing?
あの人の反論は負け惜しみにしか聞こえない。
That person's rebuttal only sounds like sour grapes.