A topic that would be interesting to investigate further, however, would be where the concept of etiquette came from. I wonder if this is yet another thing we have to study via some outsourced resource (like Emily Post's treatise or like the consultants my old law firm paid to come in and train up new associates) that in earlier times--when people were less mobile and cultures, sub cultures, and sub-sub cultures didn't mix much--would sort of be like asking a pre-modern person to define "religion."
Honestly, these days I spend most of my time socially with family and with people I've known since middle school, and whatever "etiquette" I learned in cotillion wrt place settings and how to ask a girl to do the fox trot or whatever is wholly irrelevant to the actual rules of etiquette that a Tocqueville/Herodotus/Marco Polo outsider might discern from observing how my people behave socially in reality.
OED's etymology is interesting:

There are several others further down, including as an unwritten code of conduct followed by members of certain professions, esp. medicine and law. But none of the entries predate 1737.