Antonyms are words that have opposite meanings to a given word. When it comes to the phrase "dost a bang-up job," antonyms typically connote poor or mediocre work. Words such as "botch," "bungle," "mess up," or "blunder" could be considered antonyms in this case. "Slack," "lazy," or "unproductive" might also be antonyms, suggesting a lack of effort or focus in completing a task. Alternatively, "shoddy," "substandard," or "inadequate" could be antonyms, suggesting work that falls below a certain level of quality. Knowing antonyms can help expand our vocabulary and understanding of language use.