The phrase "most no-no" implies something that is strongly discouraged or forbidden. Antonyms for this phrase could include acceptable, allowed, permitted, and permissible. These words suggest that the activity or behavior in question is not only allowed, but it may even be encouraged or praised. Other antonyms might include appropriate, proper, and respectful, which imply that the activity or behavior in question is not only allowed, but also falls within the bounds of social and cultural norms. Overall, the antonyms for "most no-no" suggest an action or behavior that is not just allowable, but desirable and positive.