I could list pages of statements that have offended me. But I'll spare us more of this exercise in uncharity, not least because what offended me was not actually any one statement. The true catalysts for my taking offense were my perception of the person who offered it, the inferences I made about her motive in speaking, the judgment I had made of her life and person, my reception of her words.
My being offended or not offended has everything to do with my relationship with the person speaking. Some of the most arguably offensive statements I've received are from a person at whom I cannot imagine being truly angry. To me, she can say no wrong, no matter how wrong are the things she says. I forgive her reflexively and painlessly, a favor she returns.
In conversation with the right person I have not only agreed with but proffered ridiculous theses, affirming the very ignorances, insensitivities, and idiocies I have scorned from the wrong people. I almost laughed out loud immediately after hearing my own voice tell someone dear to me that the care of a dog is in every way equivalent to the care of a child. Aside from the factual absurdity of this common assertion, which I have received many times with pure disgust, I HATE DOGS AND ALL WHO LOVE THEM. Except my friends with dogs. But I do hate your dogs.
So anyway, the lists of what to say and what not to say, even my own, are of limited usefulness. The true friend can say very little wrong. The acquaintance and stranger (which includes all imaginary internet people) risk a great deal in speaking. The ultimate determiner of offense is the hearer.