noun
fastidious person; fussy person; nitpicker; stickler
Describes someone who is overly particular about details, often complaining or finding fault. The word carries a mildly negative tone, implying the person is hard to please.
うちの上司はやかまし屋で、書類のちょっとしたミスも見逃さない。
My boss is a stickler and never overlooks even the smallest mistake in documents.
彼は食べ物にうるさいやかまし屋だ。
He's a fussy person when it comes to food.
Compound of the adjective stem やかまし (from やかましい, 'noisy, fussy') and the suffix 屋 (や, 'person with a certain trait or occupation').