"Extreme fan" is "극성팬"(kŭp-ssŏng-paen) in Korean.
Among the enthusiastic fan for entertainers and idol, especially it refer to that of radical fan manners bad behavior. That of such male fan 빠돌이 (bba dol e), that of female fans 빠순이 (Bba sun e). For some people to be sometimes enthusiastic dangerously, to celebrities for seek of self-restraint against fan.