Another one that comes to mind: Esmerelda Weatherwax from the Discworld novels. Formally she's Mistress Weatherwax, but most of the people in her home turf call her "Granny Weatherwax". One of the books makes it clear that this is something that only her people get to do, and that it's a rare and special honor for her to let somebody who's come from away call her "Granny".

So, since we're all from away relative to the Discworld, strictly speaking we ought to call her Mistress Weatherwax. But the narrator generally calls her Granny and by and large the fandom follows suit. I will say that I don't think I've ever seen anyone dare to call her "Esme"; that's an even more privileged circle and we all know we're not in it.