Scott Alexander traces the reasons that we can comfortably call British people “Brits” but avoid using the similar contraction “Japs” for Japanese people:
Someone asks: why is “Jap” a slur? It’s the natural shortening of “Japanese person”, just as “Brit” is the natural shortening of “British person”. Nobody says “Brit” is a slur. Why should “Jap” be?
My understanding: originally it wasn’t a slur. Like any other word, you would use the long form (“Japanese person”) in dry formal language, and the short form (“Jap”) in informal or emotionally charged language. During World War II, there was a lot of informal emotionally charged language about Japanese people, mostly negative. The symmetry broke. Maybe “Japanese person” was used 60-40 positive vs. negative, and “Jap” was used 40-60. This isn’t enough to make a slur, but it’s enough to make a vague connotation. When people wanted to speak positively about the group, they used the slightly-more-positive-sounding “Japanese people”; when they wanted to speak negatively, they used the slightly-more-negative-sounding “Jap”.
At some point, someone must have commented on this explicitly: “Consider not using the word ‘Jap’, it makes you sound hostile”. Then anyone who didn’t want to sound hostile to the Japanese avoided it, and anyone who did want to sound hostile to the Japanese used it more. We started with perfect symmetry: both forms were 50-50 positive negative. Some chance events gave it slight asymmetry: maybe one form was 60-40 negative. Once someone said “That’s a slur, don’t use it”, the symmetry collapsed completely and it became 95-5 or something. Wikipedia gives the history of how the last few holdouts were mopped up. There was some road in Texas named “Jap Road” in 1905 after a beloved local Japanese community member: people protested that now the word was a slur, demanded it get changed, Texas resisted for a while, and eventually they gave in. Now it is surely 99-1, or 99.9-0.1, or something similar. Nobody ever uses the word “Jap” unless they are either extremely ignorant, or they are deliberately setting out to offend Japanese people.
This is a very stable situation. The original reason for concern — World War II — is long since over. Japanese people are well-represented in all areas of life. Perhaps if there were a Language Czar, he could declare that the reasons for forbidding the word “Jap” are long since over, and we can go back to having convenient short forms of things. But there is no such Czar. What actually happens is that three or four unrepentant racists still deliberately use the word “Jap” in their quest to offend people, and if anyone else uses it, everyone else takes it as a signal that they are an unrepentant racist. Any Japanese person who heard you say it would correctly feel unsafe. So nobody will say it, and they are correct not to do so. Like I said, a stable situation.
He also explains how and when (and how quickly) the use of the word “Negro” became extremely politically incorrect:
Slurs are like this too. Fifty years ago, “Negro” was the respectable, scholarly term for black people, used by everyone from white academics to Malcolm X to Martin Luther King. In 1966, Black Panther leader Stokely Carmichael said that white people had invented the term “Negro” as a descriptor, so people of African descent needed a new term they could be proud of, and he was choosing “black” because it sounded scary. All the pro-civil-rights white people loved this and used the new word to signal their support for civil rights, soon using “Negro” actively became a sign that you didn’t support civil rights, and now it’s a slur and society demands that politicians resign if they use it. Carmichael said — in a completely made up way that nobody had been thinking of before him — that “Negro” was a slur — and because people believed him it became true.
