The phrase "most with it" refers to someone or something that is fashionable or up-to-date. Antonyms for this phrase would be "outdated," "unfashionable," "obsolete," and "behind the times." People or things that do not keep up with the latest trends, styles, or technologies can be described as being "out of touch," "uninformed," "backward," or "old-fashioned." Those who are not "with it" may be perceived as being dull, conventional, or conservative. In contrast, those who are "most with it" are seen as being cool, trendy, and ahead of the curve.