Chimp Out refers to the action of someone or somthing(chimpanzee) going completly ape shit on anyone who tries to calm it down. The person or thing completly looses his or her cool for an extended period of time. In extreme cases resulting in police "busting a cap in its ass".
Lady 1: " Oh God shoot the chimp shoot it (sobs)."
911 Operator: "What seems to be the problem mam?"
Police officer:"Woah man did you see that chimpanzee chimp out on that ladys ass, it ripped her face off"