The phrase "lets hair down" typically means to relax and be oneself after a period of stress, formality, or anxiety. Its antonyms, on the other hand, signify restraint, inhibition, and formality. Some of the commonly used antonyms for "lets hair down" are; strictness, discipline, reserve, formality, and decorum. These words connote the opposite meanings as they suggest the importance of self-control, convention, and propriety. The antonyms of "lets hair down" can be used in situations where composure and professionalism need to be maintained, such as in formal events, workplaces or situations that demand decorum.