Se casser la margoulette

Literally: To break one's mug

Example: “Il a glissé sur le verglas et s'est cassé la margoulette.” — He slipped on the ice and fell flat on his face.

English equivalent: To fall flat on one's face

Origin: Se casser la figure is the transparent version, and margoulette is simply another word for the same thing — Flaubert has it from 1864. Originally margoulette meant the mouth or the jaw, and only by extension the face, which is how the two became synonyms. The word breaks into mar- and goulette, the diminutive of goule, an older form of gueule (mouth). The prefix is where the etymologists separate, and two candidates hold up: it may come from margouiller, to chew, or be lifted from the Norman margane, meaning jaw. Either way the face is standing in for the whole person, since someone who falls or takes a beating does not necessarily land on it.