Pour des prunes

Literally: For plums

Example: “On a fait la queue deux heures pour des prunes : le musée était fermé.” — We queued for two hours for nothing: the museum was closed.

Origin: In Middle French a prune was not only a fruit. From the 13th century it also meant a blow, a stroke of luck good or bad, and — the sense that matters — a thing of no value at all: ne pas valoir prune was to be worth nothing, and ne preisier une prune, from the end of the 12th century, was to hold someone in no esteem. The expression grows out of that at the start of the 16th. The reason usually given is a story: that the Crusaders came home from the failed Second Crusade around 1150 with nothing but plum trees from Damascus, and that the king demanded whether they had gone all that way pour des prunes. It is a good story and probably a legend — plums were known in France since antiquity, the plum's low value was established well before the crusades some historians blame, and the likeliest reason it was worth nothing is that it was an extremely common fruit. The Damascus variety did leave something behind, though: grafted onto a local stock it produced the prune d'Ente, which is what the pruneau d'Agen is made from, and which actually comes from the Lot-et-Garonne.