The phrase "knocks oneself out" means to exert a lot of effort or work very hard. Some antonyms for this phrase include: half-hearted, effortless, lazy, apathetic, lackadaisical, lethargic, slothful, and indolent. These words convey a sense of disinterest or lack of motivation, and may indicate a reluctance to expend energy or work hard. In contrast to the phrase "knocks oneself out" which implies striving for success or making a diligent effort, these antonyms suggest a more relaxed or unenthusiastic approach to task completion.