Expression: Chercher des poux dans la tête (à quelqu'un)
Pronunciation: [sher shay day poo da(n) la tet]
Meaning: to search for any reason to argue (with someone), to quibble
Literal translation: to look for lice in someone's head
Notes: The literal meanings of the French expression chercher des poux dans la tête à quelqu'un and the English expression "to nit-pick" are equivalent, but their idiomatic meanings are somewhat different.
In French, the figurative meaning of chercher des poux is to look for a fight, something to argue about - there is a nuance of aggressiveness. In contrast, the figurative meaning of "to nit-pick" (to split hairs, get caught up in tiny details) is better translated by chercher la petite bête.
Qu'est-ce que tu as ? Tu me cherches des poux dans la tête depuis deux heures !
What's the matter with you? You've been trying to pick a fight for two hours!