Well, offensive to whom? There's obviously "Nigger"... But wait. It's offensive if a white person calls a black person that. But many a time, blacks will call each other that to 'own' the word and reclaim its power. So we have an immediate example of an offensive word that isn't offensive in many cases.
Or in recent years, simply asking "Are you a man or woman?" is offensive if they pull the 'not gender binary'-card. Yeah, we can ignore the fact that you either have sperm or eggs, or genetic anomalies that have interesting medical conditions.. But the question in certain groups is "Offensive".
Then there's the last group of people who are, what I call, professional victims. I've not seen a conservative one of these yet. They primarily are in the extremist liberal camps, and the smallest innocuous things will set them off in tirades. To them, everything they don't do is "Offensive". And this "Offensiveness" changes as per person. I usually treat these people by ignoring them. You cannot win. (An example of one of them is demanding to have others use some pronoun like hir or zir or zem. And they will get angry if you ask, don't ask, use a different one around other people or... )
Edit: I try for a variant of the Robustness Principle. Unless someone is intentionally mocking me, if they get some term wrong or use no longer "politically correct" terminology, I try to look past that for their underlying idea.