The phrase "applies oneself" typically means to put in effort or focus on a task or activity. The antonyms for this phrase would be words that describe the opposite or lack of effort.
One antonym might be "slacks off" which means to be lazy or not put in effort. Another could be "neglects" which means to ignore or fail to give attention. "Half-heartedly" or "inattentively" could also be considered antonyms as they convey a lack of thorough effort.
All of these antonyms suggest a lack of focus or dedication to a task, while "applies oneself" implies a strong commitment and dedication to achieving a desired goal.