stickler

Her grammar is fine—Ann is a stickler for grammar—and her anecdotes make sense in that they have a beginning, a middle and an end.

Maybe she's a cop who is a stickler for the rules because she's trying to impress the men upstairs.

But I ain't such a stickler for sharp-edged goodness myself nor in any way at all virtuous.

I thought you were a stickler for people keeping to their own station, and not aping their betters!