This is a street phrase used in Korea and by Koreans to refer to another Korean. The word itself has its roots in Korean currency (coin) that was often referred to as "Yupjun". It is used on an informal level and not considered to be very polite.
Mexicans call each other "guey"; Hondurans call each other "catrachos"; Salvadorans may call each other "serotes"; Koreans call another Korean, "Yah, yupjun!" ("Hey dude").
by vsudude November 29, 2010