"Being on the up and up" is a phrase used to describe someone who is honest, trustworthy, and genuine. Antonyms for this phrase could include words like dishonest, deceitful, and untrustworthy. These negative words suggest that a person is not truthful, and cannot be relied upon. Other antonyms could include words like unethical, corrupt, and fraudulent, all of which describe someone who is not operating with a moral compass. In contrast to "being on the up and up," these antonyms suggest that a person is doing something wrong or immoral, and cannot be relied upon to act in an honest or honorable manner.