From what I've heard, if you refer to a black person as "the black guy" it's rude and racist. I personally think this is bogus. How else are you going to hint at someone when making a point while you don't know their name?
And here's the funny thing, it's rude to refer to someone to what they are, and it's true. Fat people are fat people. Black people really are... black.
So, in today's society, should calling someone by what they truly are not be rude? There are MANY other ways to be racist towards someone, but referring to someone to what they truly are should NOT be racist, in my opinion.