Antonyms for "cutting the mustard" would be failing, falling short, or not meeting expectations. It is a common idiom that means to meet or exceed expectations, so antonyms for this phrase would be words that describe not meeting expectations in any way. Some other antonyms for "cutting the mustard" could include disappointing, underwhelming, inadequate, insufficient, and unsatisfactory. When someone fails to "cut the mustard," they are often seen as not being up to par or not meeting the desired level of performance or achievement. Thus, the antonyms for this phrase emphasize the opposite of meeting or exceeding expectations.