The opposite of "most bottled up" could be expressed in various antonyms, such as "open," "expressive," "outspoken," or "unreserved." Instead of hiding one's thoughts and feelings, being open means being honest, vulnerable, and communicative. Expressive people tend to share their emotions and ideas through words or actions, without fear or inhibitions. An outspoken person is not afraid to speak their mind or challenge popular views, even if it means facing opposition or criticism. Lastly, an unreserved person is genuine, candid, and courageous, resisting any temptation to hold back or suppress their true self. By contrast, the phrase "most bottled up" connotes a sense of restraint, introversion, or emotional suppression.