The term "apply oneself" refers to putting in effort or concentration towards a particular task or goal. Antonyms for this phrase would be words that describe the opposite behavior, such as slacking off or being idle. Some antonyms could include terms like procrastinate, neglect, disregard, ignore, or waste time. When someone fails to apply themselves, they may find it difficult to achieve their objectives or reach their full potential. It is crucial to remain focused and diligent in life, especially when trying to achieve success in academics, careers, or personal development.