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.