This week’s expression is, “Casser du sucre sur le dos de quelqu’un.”
It means, literally, “breaking sugar on someone’s back,” or engaging in malicious gossip about someone. In other words: backbiting, which, come to think of it, is slightly food-related too, in a cannibalistic sort of way.
For example: “Dès qu’il sortait, ses collègues se mettaient à casser du sucre sur son dos.” (“The minute he was out the door, his coworkers would start breaking sugar on his back.”)
Listen to the idiom and example read aloud:
According to these sources, this idiom appeared in the late 19th century, and may derive from the older expressions “sucrer quelqu’un”, which meant mistreating someone, and “se sucrer de quelqu’un,” which meant taking someone for a fool. Sugar was then a symbol of wealth; why it was linked to such negative notions, however, is unclear.