The phrase '手のひら返す' is fascinating because it captures such a specific human behavior—that sudden, almost theatrical shift in attitude. While English doesn't have a perfect one-to-one translation, 'to flip-flop' comes close in casual contexts, especially in politics where opinions change abruptly. More dramatic alternatives include 'to do a 180' or 'to pull a complete U-turn,' which imply sharp reversals.
In literature, I've seen characters described as 'capricious' or 'mercurial' to convey this unpredictability. Shakespeare’s 'The Winter’s Tale' has moments where characters abruptly change demeanor, though no single phrase encapsulates it. The cultural nuance matters too—Japanese emphasizes the physical gesture ('flipping the palm'), while English leans into metaphorical movement.
「手の平を返す」という表現、英語では色んなニュアンスで訳せますよね。例えば、'turn one's back on someone' ってフレーズがピッタリ来る気がします。
『ハリー・ポッター』シリーズで言えば、シリウス・ブラックが家族の価値観に背を向けたシーンがまさにこれ。最初は純血主義を信奉していたのに、最終的には完全に立場を変えています。日常会話で使うなら、'He turned his back on his old friends after getting rich' みたいな文脈で自然に使えます。
面白いのは、英語には日本語のような手の動きを表す直訳がないこと。文化の違いで、身体表現より抽象的な言い回しになる傾向がありますね。