This well-known sign with three fingers means I'm gonna kill you, or a greeting in games. It was used in the movie Happy Gilmore as Shooter McGavin's trademark. Also, the bang-bang gesture may be used to show secretly an unpleasant situation, when an annoying person enters the room. Pointing at own temple and firing with the thumb signifies recognition of own mistake. IDK is a short abbreviation of I don't know. It is part of the recently developed kind of dialect of the SMS language. VSCO Girl cursor with Bang Bang Hand and IDK.