The rules for politesse are, I think, as follows:
A community gets to choose its own name. Use of that name is friendly; use of names invented by others is at best technically accurate (and used by the politely distant), and may be a slur (and used by the hostile). The division between slur, polite and friendly is arbitrary, shifting and illogical; yet such a division is socially necessary; for there will always be friends, enemies and distant bystanders; and they need to talk.
In politesse, single syllables can cross the line. (Trans vs tranny. Yiddish vs yid.) The absurdity of politesse is a feature, not a bug; language policing is a sign and an exercise of power. This power is directed both inwardly (to dominate weaker members within the community) and outwardly (to assert the community’s autonomy to the outsiders).
Politesse is arbitrary and emotional, so it is negotiated by rhetoric, not reason. This is as it should be; reason isn’t needed, and it would interfere. The lines to not cross needn’t be rational, they need be only lines. If the lines were rational then they’d be stable, but each rising generation has to make rudeness polite in its own way.
Words can fall in and out of favor. A word’s respectability can be purchased. A word can be rehabilitated by political action. Then there’s ironic hipsterdom, where a slur’s hostility is discharged by dark humor; but this love/hate verbal tactic is best used by the obnoxious on their equally obnoxious best friends. It’s a jerk thing, non-jerks wouldn’t understand.*
Politesse is as post-modern as anything can be and still exist. It’s relative, contextual, politicized, irrational, transient, and so on. In fact I dare say that pomo was an attempt to rationally analyze present-day academic politesse; a.k.a. PC; an attempt that failed because politesse has no need for reason.
Or, let’s say, politesse has no need for contentual reason; for its contents are selected for absurdity; but it does have contextual reason. Politesse makes no sense for reasons that make a great deal of sense, just not in the terms it presents itself in.
For instance there is the matter of poesy. Rhetoric has to sound good. It needs scansion, concision, clarity and musicality. A good name should trip off the tongue and stick in the mind. Anything less is a handicap to the speaker and an insult to the hearer. For this reason I take strong exception to acronym-based names, like LGBTQQI. To such bureaucratic Scrabble-stews I retort ROTFLOL. (I propose, for an alternative, ‘gender minorities’.)
As an instance of the mutability of a name’s status: “Person of Hebrew faith” used to be a rich-German-immigrant self-name, and “Jew” was a slur. If I were in a lumber yard, and a big guy approached, bearing a broken board in one hand, and he called me a “Jew”, then yes I might get nervous. If he called me a “Kike”, then I would probably run away; but if during my cowardly retreat he called me a “person of Hebrew Faith”, or worse yet “of Mosaic Extraction”, why then I would be sorely tempted to stop, pick up a broken board, turn around and attack. (Mosaic Extraction?! What, am I a tile?) I probably wouldn’t do it, nor should, but I’d be tempted to.
* Now for a word in favor of Jerk Liberation. The Jerks are the only group of people universally despised; yet it is a group that each of us is a member of at one time or another. Since we are all, from time to time, assholes, I say that we should all respect the right of Asshole-Americans to be insufferably rude. After all, it’s a matter of identity.