Come up to snuff is an idiom that means to meet or exceed a certain standard of quality. The opposite of this phrase would be to fall short or not measure up to the expected level. Some antonyms for come up to snuff include fail, disappoint, underperform, miss the mark, be inferior or subpar. These antonyms suggest a lack of competence or meeting the required standard. To excel or exceed expectations can be synonyms of come up to snuff. It's important to note that antonyms for come up to snuff can only be used in the right context to maintain the intended meaning.