I would never be offended, so long as they don't step on Snickers, of which I have seen people do to test and see what I'd say. One of them did it about ten minutes ago in a computer lab and she saw her laying there when retrieving printouts, came back to her computer and stepped on her. I just give a sideways look and comfort my dog. No words, I believe, are necessary when that happens, as they already proved to themselves and others what they're like. It's too bad and maybe it is unintentional, but it is unfortunate.