pour des prunes

for nothing

This expression means for nothing or to no purpose, all that effort wasted.

J'ai fait la queue pendant deux heures pour des prunes, le magasin était fermé.

I queued for two hours for nothing, the shop was closed.

Tradition links this to the Second Crusade (1147 to 1149). French crusaders failed to take Damascus but brought back plum trees from Syria, and the whole costly expedition was mocked as having been undertaken just 'for plums.' The word 'prune' also meant something worthless in Old French as early as the 13th century.