I do find it acceptable when a director is in the middle of giving notes, because he's watching you portray your character, and he wants a certain something from the character, and doesn't necessarily mean the actor.
But once, two months after Steel Magnolias closed, the producer called me "Shelby". I tried to politely tell her that Shelby was my character, not my name.
The worst is when people, and I mean co-actors in the show with you, confuse you the person with your character. When I did The Crucible, castmembers actually asked me if I was sleeping with the actor playing John Proctor. And they called me a whore. REALLY?! That's my character.........If you can't tell the difference between reality and fantasy, between me the person and the character whose lines I'm reading off a page....maybe you should find a new hobby. Sorry to bitch, but it gets my goat. Please don't confuse me with the fictional character I'm portraying onstage for two hours a night.
It's the same as when, watching Harry Potter and the Goblet of Fire, someone says, "It's Edward Cullen!!" No. It's not. It's an actor named Robert Pattinson, and he's portraying a character named Cedric Diggory at the moment. Gyuh.
So I guess what I'm saying is, do your friends in your cast a favor and learn their name, and call them that when they're not onstage ;)