verb/paʁ.le d(ə) kɔʁ.d(ə) dɑ̃ la mɛ.zɔ̃ d‿œ̃ pɑ̃.dy/
to put one's foot in one's mouth, to be like a bull in a china shop, to hit the wrong note (to broach a sensitive topic in an inappropriate setting, where that topic is taboo; to be completely tactless)
Literally, “to speak of rope in the house of a hanged man”.