Koreans are people who live in or come from Korea (usually South Korea a.k.a. Republic of Korea, because most North Koreans are not allowed to travel abroad). But here we will deal with the ones in the United States of America, including those whose family currently lives in Korea.
There are all kinds of Koreans, but to name a few:
American-Koreans (so-called twinkies/bananas)
people who have spent their entire lives in America. Usually US born and second- or third-generation immigrants. They either can't speak Korean at all or understand very little of it; but they do have impeccable English speaking skills and lots of white friends. Most feel uncomfortable around other types of Koreans and/or some older relatives. Very Americanized, with no understanding of Korean tranditions or Korean pop culture. Less intense when it comes to school and work; only few of them tend to show outstanding academic performance. They all have English first names.
include Koreans who came to America as kids or those who have spent many years at American schools. Many have English first names but some choose to keep their Korean names. Good English, but their English speaking abilities depend on the number of years spent in America or the number of American friends they have. Most are academically successful and get straight A's. There is 90% chance that a given Korean-American plays a musical instrument and/or excels in math or science. Some can be good atheletes. Some have families living in Korea and go home once or twice a year; these ones develop immunities to long flights or jet lags. Although most of them are good at making friends and approachable, sometimes they might find it hard to belong to a certain social group; they often have to deal with identity problems. But there are some Korean-Americans who are completely nerdy with no trace of coolness and fail to make friends.
The ones who want to look cool and dress nicely; most of them don't. They tend to be less intelligent and less hard-working. Always in search of hot girlfriends and love fast, good-looking cars. Easy to become friends with, although some of them are cocky.
Fashionable, usually good-looking Korean girls who are rather skanky. Not as academically successful as many Koreans are, but many Asian boys or white boys with yellow fever would do anything to date them. Good dancers with good make-up skills that make their eyes look bigger; they might be shallow. But party on.
The very Korean ones who just arrived in America. They have thick accent or do not speak much English and like to play their Korean music. They don't really participate in atheletic events or social gatherings. No dance parties. Usually hang out with other Koreans or Asians with accents. Despite their rather horrible English speaking ability, they are amazingly expert in English grammar. Even better in mathematics, physics, and chemistry. Basically the only mathematicians who can beat them are either Chinese or Indian. Very competitive people who sometimes appear to be selfish, but many are actually nice and straighforward.
(There are many individuals who do not fall into any of these categories. Each and every one of these individualities, which only have their Korean-ness in common, should be respected. These are just streotypes I came up with to make the article interesting.)
A: Where are you from?
B: I'm from Seoul.
A: Oh, is that in China or Japan?
(If you're a Korean you might want to stop wasting your time talking to someone so ignorant.)
B: It's the biggest city in Korea. (and pretty awesome)
A: Are you from North or South Korea?
(Now is the time to leave.)