The phrase "lets it hang out" is associated with the idea of being carefree, relaxed, and expressive. Antonyms for this phrase would include being reserved, timid, or rigid. If someone is not comfortable in their own skin, they may be guarded and closed-off from others, not allowing themselves to be vulnerable or open. Conversely, those who "let it all hang out" are not afraid to show their true selves and are often seen as genuine and authentic. To be the opposite of this would mean being detached or distant, hiding one's emotions and thoughts, and maintaining a sense of control over their behavior.