This is an interesting question. I'm not going to comment on facial features because those tend to throw people off. I'm a Chinese descent, but I don't have a flat/slanted face, tanned skin, or small or puffy eyes. Anyone who is trying to determine anybody's ethnicity through facial features doesn't know what they're talking about. Besides, there are 56 Chinese minorities, so there is no way you can use facial features to classify them.
The easiest way to differentiate them is by the last name, language, behavior, and clothing. If you're trying to tell Asians apart in a place like the US, its pretty hard based on physical appearance.
As far as behavior, I know its common for Asians to "bow" when greeting people, so I guess you can tell by how they take a bow. Based on my observations, Japanese (women in particular) look like they bow to a 90 degree angle with their hands together in front, Koreans look like they bow to a 45, and Chinese just slightly bow their heads. As for Vietnamese...I have no idea (do they bow?).
The method I use to determine their nationality is through the accent, and to determine their ethnicity, I just observe the last name and how they behave around their own family.
As for your friend, I really don't know because I have to see him in person and observe his behavior to know.
I'm Asian and have traveled in a lot in central Asia.
· 1 decade ago