Se faire du mouron

Literally: To give oneself some hair

Example: “Ne te fais pas de mouron, elle a juste oublié de charger son téléphone.” — Don't lose sleep over it; she just forgot to charge her phone.

English equivalent: To lose sleep over something

Origin: Gaston Esnault dates it to 1948, which is recent for one of these. Mouron is the plant chickweed, but in slang since the middle of the 19th century it has meant hair, and that is the sense at work — se faire du mouron is se faire des cheveux, to give oneself hair, in a coarser register. The neighboring expressions run the same way: se faire de la bile (to make oneself bile), se faire du mauvais sang (bad blood), se faire un sang d'encre (ink-black blood). Strictly, worry makes people tear their hair out rather than grow it, which looks like an objection until the fuller original turns up — se faire des cheveux blancs, to give oneself white hair, which is exactly what worry does. The short form is an ellipsis of that.