The phrase "letting it all hang out" typically means expressing oneself in a relaxed and uninhibited manner. Antonyms to this phrase can include being reserved, cautious, guarded, or restrained. People who are guarded tend to be cautious in expressing their feelings or thoughts, often holding back for fear of being judged or misunderstood. Being reserved may mean the person is shy or introverted in nature, and may not easily open up to others. Being cautious may suggest a sense of practicality and calculated behavior, rather than being impulsive or reckless. When someone is restrained, they may be holding back due to social conventions or a desire to maintain appearances.