Dear Miss Manners: I am writing about an etiquette problem common in historic re-enactment/living history groups: people who are popularly known as "authenticity police."
Authenticity policing takes the form of walking up to another person, closely inspecting their clothing (even lifting up skirts to examine underwear), then informing them that they "ought to" have used natural fibers, or hand-sewn their seams, or that they are "too old" to wear a style, or that "you shouldn't wear vintage clothing because you're destroying a part of our history."
They feel authorized to personally evaluate the reproduction (or antique/vintage) clothing of fellow members and event attendees for "authenticity" or "accuracy." This is in addition to, and usually well beyond, any official standards or requirements that may be imposed by the organization.
Authenticity police insist they are being "educational," "scholarly," even "helpful." Sometimes the information they give is correct; sometimes, in my opinion, it isn't. Either way, their unsolicited criticism is primarily one-upmanship and pressure toward social conformity.
Because I am interested in history and historic costume, I enjoy re-enactment activities in concept (though not some of the re-enactors). I have not found a solution to this problem other than to tell the "authenticity police" to mind their own business.
I do think modern etiquette should apply to this situation, because socially these are modern groups. Besides, Miss Manners might not approve of the etiquette that would have been used in some historic eras, for example, physically assaulting the criticizer.
Gentle Reader: No, but neither does she care for the modern assumption that it is acceptable to go around insulting people. Officious types who behave dreadfully to improve society have always been among us -- as have those who make self-righteous excuses for lifting women's skirts -- but their victims were not always so willing to stand still for them.
Miss Manners would advise responding with a nice old-fashioned statement from whichever period the group re-enacts, along the lines of "How dare you question my honor!"