The antonyms for the phrase "most unbuttoned" include "buttoned up", "refined", "elegant", "neat", "tidy", and "polished". These terms describe someone who is well put-together and maintains a sense of professionalism and decorum. The opposite of unbuttoned clothing, for example, would be clothing that fits snugly, has all of its buttons securely fastened, and looks neatly pressed. In a social setting, someone who is buttoned up may be seen as reserved or even uptight, but they maintain a certain level of class and sophistication. Overall, the antonyms for "most unbuttoned" are terms that describe someone who is well-mannered and in control.