The phrase "knock oneself out" generally means to exert oneself to the point of exhaustion or to go to great lengths to achieve something, often with a lot of effort. Some antonyms for this phrase are "take it easy," "relax," "rest," and "take a break." These words suggest the opposite approach and imply that one should slow down, preserve energy, or take a hiatus from hard work. Another antonym could be "give up" or "quit," suggesting the complete abandonment of an undertaking or the decision not to bother trying at all. In essence, the antonyms for "knock oneself out" suggest avoiding overexertion and finding a more leisurely pace.