The phrase "most in to" refers to something that is popular or trendy. Antonyms for this phrase would be words that describe something that is outdated, unpopular or unappealing. Some possible antonyms for "most in to" include unfashionable, antiquated, uncool, outdated, unpopular, old-fashioned, unhip, and passe. These words can be used to describe anything from clothing and music to gadgets and hobbies that are no longer in vogue. While some people might still appreciate these things, they are generally not considered to be the "most in to" of the moment.