"Going ape" is an informal slang phrase used to refer to someone who is behaving uncontrollably or losing their mind in a fit of rage or excitement. However, some antonyms for this phrase could be "calm", "composed", "restrained", "serene", "tranquil", "collected" or "level-headed". These words indicate a sense of control and maturity that are the polar opposite of "going ape". So, when you feel like you are about to lose control or behave erratically, take a deep breath and strive to be identifiable with these antonyms rather than "going ape".