A recent popular Korean tv serial "teach you a lesson" became wildly popular despite being not-so-politically-correct, precisely because of the severity of the problem.
highly recommend you watch it.
They are generally less friendlier than all the other foreigners I met, closed to outsiders, and somewhat racist (I asked a group of Koreans if I could join their game of Basketball, but they said they preferred to play by themselves. No Chinese ever said anything like that, nor any other foreigners I had joined to play with).
Also, they are quite a violent people. My classmates and I nearly came to blows over the window in the class; I wanted to open it because the indoor air was stale and probably toxic, but he didn't want the window open (for whatever reason, though the weather wasn't cold). Another non-Asian foreigner got into a fight with a Korean puncturing his eardrum which resulted in deafness. Outside the university, too, when they get drunk they become aggressive and seek fights. I guess it must be all the stress they're to put up with in their Dystopian country?