The antonyms for "be proficient" are to be unskilled, inexpert, amateurish, incompetent, and unqualified. These words are used to describe someone who lacks the necessary skills or experience to perform a task effectively. Being unskilled implies a lack of training or knowledge, while inexpert suggests a lack of aptitude or aptness. Meanwhile, amateurish implies a lack of professionalism or polish, and incompetent conveys a level of incapacity or lack of ability. Lastly, unqualified refers to someone who lacks the necessary credentials or qualifications to perform a task. Overall, these antonyms emphasize the opposite of proficiency, indicating a level of inadequacy or lack of competence.