Description from here: http://www.rjkoehler.com/2011/08/29/to-foreigners-in-korea-please-learn-a-little-korean/

"A video is circulating on the Korean Internet of a black gentleman yelling at and threatening an elderly Korean couple.His violent behavior was the result of him misunderstanding the elderly man’s comment to him. The elderly man reportedly said “니가 여기 앉아” (a sign of consideration) ("You can sit here" = Niga Yuh gi anja"), but not knowing Korean, the man in question interpreted “니가” as the N-word which led to his violent outburst.
[...] Apparently our culprit learned “개새끼야” but couldn’t be bothered to learn simple pronouns. Definitely North American, but if his hair is any indication he’s definitely not a soldier."
Thank goodness for that.

Update: Another account I found holds that "as far as I know, the old korean man just told him to keep it down because he was talking so loud on the phone. It infuriated the black man, and then started swearing. Later, the old korean man said "니가(nigga)" which in korean means "you," and the black man who doesn't speak Korean thought he was insulting him and started beating him up."