Being in on refers to being privy to information or involved in a situation. The antonyms for this phrase would be being out of the loop or being unaware. If someone is out of the loop, they have no knowledge of the situation or information. Similarly, if someone is unaware, they lack knowledge or understanding of a particular matter. Being excluded, excluded from the conversation, or uninformed could also be considered antonyms for being in on. In conclusion, understanding the antonyms for "being in on" can help us accurately describe our level of knowledge or involvement in a situation.