The phrase "knocking oneself out" is commonly used to describe a situation where someone is putting in a lot of effort, often to the point of exhaustion. However, there are several antonyms to this phrase that indicate a lack of effort or energy. One such antonym is "taking it easy," which means to relax and not push oneself too hard. Another antonym could be "slacking off," which means to not work as hard as one should. "Procrastinating" is also an antonym, as it implies putting things off until later instead of doing them immediately. Overall, these antonyms indicate a lack of motivation, energy, or commitment.