Rouler dans la farine is a colloquial expression that translates literally as rolling in flour. The expression is commonly used in the reflexive causative – se faire rouler dans la farine – to be swindled, cheated, to get ripped off, or rouler quelqu'un dans la farine - duping/fooling someone, playing a trick on them, or using one’s wits and lies to take advantage of someone who is a little naive.
The verb rouler on its own informally means to cheat, to deceive - in addition to its regular meaning to roll. Then, one might ask, what's the flour about?
The expression dates back to the early 19th century. Rouler already had the figurative meaning of cheating on someone at that time. La farine on the other hand symbolized lies, or misleading arguments, presumably in relation to the fact that actors then used it as stage makeup. The expression "rolling someone in flour" added emphasis to the mischief at hand by providing a strong visual of one being "rolled in deceit." It also added a notion of ridicule: the gullible victim is somehow responsible for letting himself be fooled so easily and thoroughly.
In the flour department, note that the verb enfariner - to roll in flour, can also be used as a synonym for the expression. It was first used by Jean de la Fontaine in his fable "Le chat et un vieux rat - " The Cat and the Old Rat." In the story, a cat "s'enfarine" - i.e. covers himself in flour - and hides in the bread hutch in order to catch mice. Overconfident in his success, the cat hadn't thought that the old, experienced rat wouldn't be fooled. Today the adjective enfariné means both looking half asleep and looking naively overconfident.
J’ai trop payé pour cette voiture pourrie. Je me suis fait rouler dans la farine!
I payed too much for this piece of junk car. I got ripped off!
C'est tellement désagréable to s'apercevoir qu'on a été roulé dans la farine par quelqu'un en qui on avait toute confiance!
It is so unpleasant to find out you've been taken for a ride by someone you trusted!
When Jacques Chirac was président de la République, it was sometimes cheekily said that his Prime Minister Jean-Pierre Raffarin “roulait la population dans la raffarine”.