We don't need to refer to a librarian that way. Yeah, I know, Seinfeld did it. It isn't funny or interesting. It is a cliché. Let's try to choose our language so that our history and language can hold onto meanings that matter.
That person isn't "meek" usually, though. They are very clear that they have the power and you will obey them. They are very insistent, without ever having to get loud, and they will force you to follow the rules.
I don't have another word for that kind of person, but I agree that "nazi" should not be used that way.
There is a Star Trek TNG episode called Darmok that describes a culture that only speaks in metaphor. https://en.wikipedia.org/wiki/Darmok
Surely we have a better metaphor for a meek but powerful librarian than ...
> Who will be the library nazi that kicks you out when you talk too loudly?