Professor Stairs recently addressed a question about the difference between 'immoral' and 'impolite' where, if I understand him correctly, he basically said that there's a fact of the matter about morality, whereas norms of politeness are society-relative.
But I think it's worth pointing out that there are a variety of other views about morality: for instance, relativism, error theory, and even some views where moral claims aren't considered truth-apt (as in logical positivism).
May I ask Professor Stairs a potentially more interesting question: assuming relativism, or some similar view where there is no universal moral fact of the matter, is there a bright-line difference between the immoral and the impolite?
Perhaps not a bright line. But let's take relativism as our foil, where we understand relativism to mean that standards of evaluation are relative to norms, traditions, etc. of societies or groups. (I'm paraphrasing a definition from https://plato.stanford.edu/entries/moral-relativism/ ). If that view happens to be correct, notice that it doesn't leave us without a distinction between morals and manners. Even if relativism is the right meta-ethical view, we still make a distinction within this society (US society for the sake of example) between matters of politeness and matters of moral right and wrong. Close enough for our purpose, we Americans agree that stealing is wrong and not just rude. We also agree that showing up to a wedding in ragged shorts and a T-shirt is rude but not really a moral wrong (though see below). The line between the two cases seems to be something like this: we can imagine, though we might not find it an attractive prospect, that fashions might change and showing up to a...