Acquits oneself means to perform a task or duty satisfactorily or to behave in a proper or discreet manner. The antonyms of this phrase could include performing poorly, misbehaving, making mistakes, disappointing oneself or others, or failing to meet expectations. Other synonyms could include bungling, fumbling, stumbling, or botching a task. The opposite of acquitting oneself well would be to "discredit oneself" by behaving inappropriately or unprofessionally. It is important to take ownership of one's actions to avoid negative consequences, and to strive for excellence to earn the trust and respect of others.