Prendre la mouche
The expression prendre la mouche literally means to take the fly. No, it doesn’t involve a bizarre new diet. Rather, it describes that moment when someone gets unexpectedly upset or takes offense over something that seems trivial. It’s like watching someone trip over a blade of grass and explode in rage. A French equivalent might be se vexer pour rien, which translates to getting offended over nothing.
Origin
This little gem of a phrase dates back to the mid-17th century - though its cousin "prendre mouskes" was buzzing around as far back as the 14th century. Back then, "mouche" referred to all those pesky flying insects that drive us nuts, such as flies, wasps, and the dreaded horsefly, the original instigator of drama.
Anyone who has ever wandered into the depths of the French countryside may have sometimes noticed, in a nearby meadow, that a cow has suddenly gone somewhat crazy, running and mooing through its pasture, like it just found out the grass isn’t organic. Naturally, you think, "What on earth has gotten into it?" Well, imagine you’re that cow, happily grazing when a mischievous horsefly decides to land on a very sensitive spot. In that context, it’s easy to see why the poor bovine freaks out. But from the outside, it just looks like a cow having a meltdown over... nothing!
To add a bit more flavor to this expression's history, it's worth noting that in the 16th century, "mouche" also referred to a sudden thought or worry, proving that even back then, people could get all worked up about things buzzing in their heads!
Examples
Quand je lui ai dit que son projet avait besoin d'améliorations, il a pris la mouche et a commencé à se fâcher.
When I told him that his project needed improvements, he got upset and started to get angry.
Il est tellement susceptible qu'il prend la mouche pour un rien.
He is so sensitive that he gets upset over nothing.