翻脸 literally means 'to flip one’s face'—a vivid idiom describing a sudden, dramatic shift in facial expression, usually from friendly or neutral to angry, cold, or hostile. The character 翻 (fān) conveys reversal or flipping, while 脸 (liǎn) means 'face' but here stands for one’s outward demeanor or attitude. Together, they capture the physical and emotional abruptness of turning against someone.

This phrase is almost always used in interpersonal contexts: it signals the breakdown of a relationship, a heated argument, or the moment trust collapses. It implies intentionality and emotional intensity—not just feeling upset, but visibly and decisively changing how one treats another. While it can describe a fleeting expression change, it most commonly indicates a lasting rupture, such as ending a friendship or business partnership after a betrayal or disagreement.