Sometimes you are trying to give a description of how a person looks, whether it is for a story you are writing, a description of a person whom you are attempting to tell another person that you just saw (because they were cute, had a interesting tatoo, was your waiter, or robbed a bank or whatever), but because I am white, it always seems awkward or wrong or racist to other people to dare to describe someone as black or an African American. Because I am white, using that term is merely to differentiate whom I just saw, not to be offensive in any way.
If I am in a room full of mostly white people and I’m trying to tell my girlfriend that I just saw this cute guy, or that a particular person was our waiter, or that someone had an interesting tatoo, or I just saw someone rob a bank, if the person was black, that term (or African American) is more clear. If it was a white person that I was trying to describe and I was in a room full of white people, using the term white wouldn’t be very helpful and I would have to use more descriptions. But if you just say, “Hey I just saw some a really cute guy” and your friend asks which one, if you are in a room full of mostly white people, it just makes more sense to say “That black guy over there on the bench.” It’s not racist, it’s just a description.
If that same cute guy was white and you were in a room full of mostly white people and your friend wanted to know who you meant, you probably wouldn’t even say that he was white. You would be more likely to say, “That guy over there on the bench with the brown hair and the baseball jersey, the green baseball jersey, not the red one.” But if there was only one black person over there, and he was the cute guy, then it would just make more sense to just say, “That black guy over there on the bench.” But people get all bent out of shape about it.
And like one of the other posters pointed out, not all black people (even in the U.S.) are African-Americans. Sometimes all you are doing is describing someone, but if you don’t use the right terms at the right time people get very upset.
If I was in a room full of mostly black people and I saw a cute guy (that was black) I would then have to use the longer desription, “That guy over there on the bench with the green baseball jersey, not the red one.” If the cute guy in the room at this party were white, then I would probably say, “That white guy over there on the bench.” None of these descriptions are meant to be hurtful or rude or racist. They are just meant to quickly differentiate one person from another in the most obvious way.
And if my girlfriend was black and I was pointing out a cute guy that was also black, but everyone else in the room was mostly white, it would make more sense to say “The black guy on the bench.” It would make less sense (in this example) to simply say, “The guy on the bench with the dark brown hair and the green jersey, not the red one.” Because then she would likely ask, “You mean the black guy?”
I used to work with a pretty equal mix of people from different races and backgrounds and because we often had to point out to a security guard or other person in authority what we just saw, it made reasonable sense to say “The black woman with the green hat” and descriptions have been given to me in exactly the same way, “It was the white woman with the green hat.” In these cases, no one is meaning to be rude or racist, but simply using racial terms often makes people uncomfortable, even when it’s just a description.