I'm intrigued by a story out of Nova Scotia about a Mi'kmaq woman who filed a complaint with the Nova Scotia Human Rights Commission back in 1999. Dorothy Kateri Moore was working at a sports store in Sydney when her boss referred to her as "kemosabe". Apparently this boss, who knew the term from 1950s television because it's what Tonto called the Lone Ranger, believed it meant friend.
It's safe to say Moore's boss acted with a certain lack of sensitivity and should have known better than to apply the term "kemosabe" to a woman merely because of her race, but is it a racial slur? Personally, I don't think so. Whenever it was used on that television series, it was used in a friendly, respectful manner. A racial slur is derogatory and meant to cause hurt.
I'm a white, Catholic male of Irish descent. If a boss, in a friendly manner, began calling me "magically delicious" because a leprechaun used that phrase on television, I might find it annoying and perhaps a little creepy, but I wouldn't see it as a slur. Calling me a drunkin', fightin' potato eatin' bum, however, would be a different story, although I'd be cool with it so long as I wasn't called late for dinner.
I couldn't tell you exactly where the line is, but I know it when I hear it.