Put on one's thinking cap is a common phrase that implies the act of focusing and using one's brainpower to come up with an idea or solve a problem. However, there are several antonyms for this phrase, including switching off one's brain, being clueless or unintelligent, and avoiding the task at hand. When one does not put on their thinking cap, they may be considered lazy or uninterested in the task at hand. Additionally, they may not be able to provide innovative solutions or ideas, as their lack of focus and thoughtfulness may limit their creativity. Therefore, it is important to put on one's thinking cap to approach challenges with a fresh perspective and a motivated mindset.