I usually go by the way they dress, as I said, japs were more surfy types and tend to go with more cool gear, jap girls on the other hand are hard to pick out, but they are usually the ones with the wackiest accessories.
Korean guys tend to go for the more mature glammor look, and they pull it off quite well! Korean girls are usually the ones with the most make up and big big big big arse bags that could hold my whole living room.
Chinese guys look like big boys, they try too hard to impress, (think skinny jeans for guys *shivers). They are either the geeky type who live in an internet cafe, the player wannabe with the big diamond earing and skinny jeans, or the sporty type forever with a shirt and bball pants on. Chinese girls either look made up like a doll, or don't care about their appearances much, not too much in between.
Indonesian boys are forever in flip flops, even if they are wearing semi formal attire on top.
Philo boys try too hard to be white, while philo girls are usually the more stuck up than the other asian population.
Viet boys tend to be shorter and usually have this semi gangster wannabe style, viet girls are usually very pretty but tend to be on the shorter side.
Basically I couldn't tell the difference between the different asian cultures if you just gave me a picture of a face, but their general attitude and body language usually gives away hints about their origin. And since you can't be racist to your own race, I'd just like to say Chinese boys (not the abc ones) totally suck on the taste scale when it comes to dressing themselves teehee