Francophonie· medium
monter sur ses grands chevaux
“to get up on one’s big horses”
Meaning
To react with sudden indignation
Explanation
Used when someone gets huffy or blows things out of proportion over a small slight, the French equivalent of getting on your high horse.
Example
Il est monté sur ses grands chevaux dès que j’ai posé la question.
He got all indignant the moment I asked the question.
Origin
Goes back to medieval warfare, when knights rode large war horses called destriers into battle rather than the smaller horses used for everyday riding. By the late 16th century, the image of charging off on a big warhorse had shifted to describe someone losing their temper.
Source