My roommate who is white took a course on "White privilege". One interesting thing she learned in that class is that when most people refer to a white guy, they just say say "guy". By default, the guy is white. Race is only used as an identifying factor when the person of interest is not white. This trend is actually very apparent in journalism. Just read the news and see how often the word "white" is used in identifying a person versus "black", "asian", "hispanic", or even "muslim" these days. So in that sense, I suppose I understand why someone may be offended by you using "black" as an identifying factor for that guy 
That's a really interesting point. But it can go either way. In Japan, they most likely do not refer to each other as "that Asian guy". But if there's a white person, they would probably say "that white guy". But I'm no expert on Japan It just seems like common sense that the way a person is referred to is relevant to where they are in the world.
It just seems like common sense that the way a person is referred to is relevant to where they are in the world.
Wait... Asians are not white? So thats why I've never seen a "black asian" person! Because THERES NO SUCH THING. Thanks to make me learn! It wasnt obvious because (Haven't you noticed?) asians' skins are just as white as white people's! Don't u think? LOL