We’ve discussed similar matters before but not all together, clear of other material.
It’s odd that some words, seemingly neutral in origin, have come to be ethnic slurs. I’m specifically talking about terms that derive directly from acceptable, neutral national identifiers: not talking about Black or Gook or anything like that.
Polack is basically a deadset transliteration of the Polish word for Polish person, but it is unequivocably offensive when used in English.
Some shortforms are not acceptable. Jap is considered inappropriate, though perhaps not offensive to the same extent. Similarly, Iti, Nip. In the UK, I gather, Paki is considered a term of abuse, whereas in Australia it is no ruder than Aussie: just a short form. There are some borderline terms in Australian English that would probably depend on how they were said and who was saying them: Lebbo, Gyppo.
But that’s a different matter. Abbreviation could be considered disrespectful. On the other hand, it is not always. No one thinks of Aussie or Brit as offensive terms.
I wonder how words, starting as very straightforward and obvious national identifiers, become abusive terms. I suppose it would have to happen gradually. Maybe if the people in question are referred to in a derogatory way most of the time, the derogation becomes stuck to the noun itself. It would be hard, I suppose, to trace the “feel” of the word just by looking at literature.