Bang-up is a slang word used to describe something that is excellent or impressive. Its antonyms are words that convey the opposite meaning of "bang-up." Some of its antonyms are mediocre, poor, bad, awful, and unsatisfactory. These words have negative connotations and indicate that something is of low quality or standard. Other antonyms include disappointing, dismal, lousy, and subpar. These words are often used to describe things that fall short of expectations and are not up to par. So, while bang-up is a great word to describe something, its antonyms help us describe things that are less than great.