Francophonie· medium
prendre la mouche
“to catch the fly”
Meaning
to get offended suddenly
Explanation
It means reacting abruptly with irritation to a remark or situation.
Example
Il a pris la mouche pour une remarque pourtant banale.
He got offended over what was actually a trivial comment.
Origin
It most likely comes from watching animals in the countryside who would bolt when bitten a stinging fly.
Source