One thing we can, or should, all agree on is an admittedly elusive something called variously, Moral or Social Equality:

Whoever we're sitting next to, or across from, or even round the corner from--whatever their age, sex or condition--while they share with us a common table, all are our moral and social (even intellectual) equals, and our friends.  We hold religiously to this, or else, with our food untasted and our wine unsipped, we must excuse ourselves as unobtrusively as possible to our host, and, without making any fuss whatever, depart, both from the hospitable board and from the house that offers it.  For the honors of the table and the hearth are sacred, and he who violates them, and even he who only neglects to hold them in due respect, deserves exile and death.

It is to the Greeks, that I know of, that we owe the first codification of the laws of Hospitality, but, certainly, they are as old as mankind, and may be seen, meticulously though wordlessly observed, in the ordinarily civil behavior of our nearest relative the Bonobo Chimpanzee.