The phrase "am on one case" implies that someone is focused on a particular task or assignment. In contrast, antonyms for this phrase include "unfocused," "indecisive," and "distracted." These antonyms suggest that someone is not fully engaged in their work and may be easily sidetracked. Other antonyms could include "unconcerned," "indifferent," or "uninterested," which imply a lack of investment in the task at hand. While being "on one case" may be a positive trait, it is important to be aware of these opposing terms to better understand how one's work habits are perceived by others.