En faire tout un fromage

Literally: To make a whole cheese out of it

Example: “Ce n'est qu'une petite rayure sur la voiture, pas la peine d'en faire tout un fromage.” — It's just a small scratch on the car; no need to make a big deal out of it.

English equivalent: To make a mountain out of a molehill

Origin: 20th century, and the joke is in the transformation rather than the cheese itself: milk is about as plain and unremarkable a starting point as food gets, yet it can be worked, through real skill and real time, into something as elaborate as a fine cheese. Making a big fromage out of something is therefore building an production out of raw material that did not call for one. Fromage itself has a longer trail behind it — Greek phormos gave Latin forma (a mold, a shape), which produced fourmage, then fromaige, settling into its modern spelling only in the 15th century.