"Knowing one's stuff" is a common expression used to describe someone who is knowledgeable and skilled in a particular area. The antonym for this phrase is "ignorant" or "uninformed." Someone who is ignorant lacks knowledge or understanding of a particular subject, while someone who is uninformed simply lacks knowledge about a specific topic. Another antonym is "uncertain" or "unsure," which describes someone who is not confident or knowledgeable in their abilities. Additionally, "incompetent" or "inept" describe someone who lacks the necessary skill or knowledge to perform a task effectively. In summary, the antonyms for "knowing one's stuff" include ignorant, uninformed, uncertain, incompetent, and inept.
