The antonyms for the phrase "acquitted oneself" primarily involve failure, incompetence, or unsatisfactory performance. Such antonyms can include phrases like "failed to deliver," "fell short," "underperformed," or "disappointed expectations." When someone has not acquitted themselves well, they may be described as "inadequate," "inept," "clumsy," or "ineffective." Negative phrases like "didn't measure up," "fumbled their opportunity," or "dropped the ball" can also be appropriate antonyms. Overall, the antonyms for "acquitted oneself" describe a situation where an individual was not able to perform to the expected level and failed to demonstrate their skills or ability.