Flub up is typically used to describe a mistake or error that has been made. Antonyms for flub up would be words that describe successful actions or outcomes. For instance, words such as accomplish, achieve, succeed, or excel could be considered antonyms for flub up. Similarly, terms like flawlessness, perfection, accuracy, and exactness could also be used as antonyms, indicating a successful and error-free outcome. Regardless of the specific antonyms used, all of them carry a positive connotation and imply that a person has done something well, expertly, or without error, which is the complete opposite of flubbing up.