The phrase "most tip-top" means the highest level of excellence or perfection. Its antonyms would therefore be words that convey the opposite meaning. Some possible antonyms for "most tip-top" could be "worst," "inferior," "inadequate," "deficient," or "substandard." These words suggest a lack of quality, performance, or effectiveness, in contrast to the superior level of quality implied by "most tip-top." Using antonyms for "most tip-top" can help to create contrast in writing or speech, emphasizing the importance of achieving excellence or avoiding mediocrity.