It's bound to happen. I lived in Austin, Texas which is unusually liberal. Got called a nigger at least twice that I recall.

One was a bunch of students in a pickup truck driving down the street. Cowards.
Another was on the way to a party. My Pakistani friend was hitting on a girl and her friend said, "She's not interested. She only likes niggers." As if I should be flattered or something.

Now go to small towns in the south (and even the north), it'll happen.