My wife tells the story of one of her Canadian/Irish relatives who was doing some kind of public health stuff in Nigeria. The family was a bit concerned when he announced that he had gotten engaged to a woman that he met there; after all, Nigeria is just full of Them. When she came to Canada and the family was able to see that she wasn't one of Them, they were pleased to welcome her to the family; everybody thought that she was a delightful person.
What's unusual about this story? Well, with this family "Them" is Protestants. When she went to Mass with the family, everybody gave a sigh of relief. Her skin tone? The kind of rich, velvety West African black that drives photographers up a wall. ("Expose for the skin tones". Yeah. Right.) For this family, irrelevant.
A nastier version happened when my wife and I visited my father (the first and last time). After getting my father off of his normal topic of conversation (Rush Limbaugh is God), his wife went to work. She went into her full tirade about how horrible They are. When she gets into this mode, you're in for about a half hour of high volume ranting and raving. In her mind,They are filthy, diseased, ignorant, stupid criminals who have no right to exist in a civilized society. I had long since learned to let her vent; if there's anything that will shut her off, nobody's found it. (I never tried a bucket of cold water.)
Problem is, to her, They are Italians. And my wife's father is first-generation Italian-American. My wife is one of Them. They have an English name because in the 1930s, her father found that a machinist with an Italian name was unemployable, while the same machinist with an English name could get a job anywhere.
Anyway, we walked out and never went back. I suspect that they have no idea why we got offended. At least, nobody on that side of the family has ever contacted us.
Life Lesson: Everybody has a Them. Everybody's Them is different. You are part of somebody's Them. And the person you're talking to may be one of your Them.