The act of going so hard that you lose all the ability to walk, speak and think properly. This phenomenon often occurs after drinking too much alcohol or using too much drugs. People who are "going ape" can often only think about sexual intercourse. Activies like sleeping in random spots, puking excessively and urinating in inapproriate places are not exceptional.
Bob: What's going on with Martin?!
David: Oh don't mind him, he decided to go ape.