Nitpicking is the same idea as nit-picking, written as one word: finding tiny faults and treating them as important. It can name the habit (“I am tired of the nitpicking”) or describe a comment (“a nitpicking remark”). Informal, and usually a complaint. The picture still comes from picking nits — tiny louse eggs — out of hair, one by one. Though actually, English has not settled on one spelling. Hyphen, one word, even two words turn up; learners’ books often show nit-picking and nitpicking side by side. The meaning does not change. Use it when you want to say the fuss is too small, not when you only mean “careful checking.”

吹毛求疵；挑剔小毛病