For me, the only reason I need for why it's inappropriate behavior is that it made me, and probably other people around me, feel shitty for something that has nothing to do with me, or someone else. Now, If the person apologizes and said they made the mistake, I can let it go, but if they keep on insisting they did nothing wrong, that's going to bother me.
Boiled down, the reactions of the other person are essentially what matters. I don't think it's so much about being fake as it is about creating win-win scenarios, or in a maybe more developed form like that of fia it can be about balancing the needs of the few with the needs of the many.
Although sometimes, it can be about letting others know that you aren't going to let them intimidate me. Because in some situations, this is the only thing people respond to, unfortunately. A fun way to do this is just through honesty, and just pointing out things I've noticed about them that conflict with their self-image or world-view. It sounds a little harsh, maybe, but acting on this allows me to let go of whatever anger I've been feeling and move on, and creates a space for reconciliation (for myself, anyway.)
And, if nothing else, it usually gets people off my case because the realize that I can bite back.