The phrase "give a good account of oneself" means to perform well or satisfactorily in a particular situation. Antonyms for this phrase could include "falter," "underperform," "disappoint," "fail," or "struggle." These opposite terms suggest a lack of success, proficiency, or capability in a given task or endeavor. They convey a sense of weakness or inadequacy, rather than the strength and competence implied by "giving a good account of oneself." When facing a challenging situation, it is important to strive for the positive antonym of this phrase, and to work towards achieving success and demonstrating one's abilities to the best of their potential.