To defeat Bushwacker you must do two things. First, aim for his head and fire. Eventually, his glasses will fall off. Once, his glasses are off it is a free for all as long as you have some flashbangs. If you do not have flashbangs, then just kill some henchmen and they will drop some. Begin launching flashbangs near Bushwacker and he will get disoriented. When he starts moving around like he is drunk, start shooting him. He will begin to fire his weapon, but most of the time he is inaccurate. He eventually will die after enough damage is taken.