I guess the distinction I would draw is that reasonable discussion is required. If I have never heard before that “gypped” is an offensive term, under a reasonable person standard, I shouldn’t be criticized for using it. But once I’ve been informed that it is offensive, it seems to me that the standard changes.
I think it’s interesting to consider the mini-sombrero case in the light of what the party organizers knew. I think the wording of their invitation strongly suggests that they weren’t really surprised to learn that some aspects of the party offended some people.
Let me add: as I think I said above, in my opinion, avoiding offending others unnecessarily is valuable in itself, so I don’t think the end of the story is whether a “reasonable person” would find this particular thing offensive. I think if somebody actually does find it offensive, then the right thing to do is to consider whether there is any countervailing reason to do it. I will say that countervailing reasons could include the fact that many people like to do it, and that it isn’t deemed offensive by many people (including other people who are similar to the offended person). This is why the name of the Washington Redskins is still controversial–it’s clearly offensive to some people, but some other similar people aren’t offended, and a lot of people like the name because of (I guess) tradition. Personally, I would change the name if the decision was under my control–but there are other situations in which I would go the other way. Again, nobody should pretend that these line-drawing exercises are easy.