"Got down pat" means to perfect or master a skill or knowledge. Antonyms for this phrase would be words that describe an inability to learn or perform well. These could include "incompetent," "clumsy," "inefficient," "inept," or "awkward." They all suggest a lack of skill or ability to perform tasks well. Alternatively, some antonyms could include "novice," "learner," or "beginner," which would all indicate someone who is still in the process of acquiring skills or knowledge. While "got down pat" suggests a high level of proficiency, these antonyms suggest the opposite - a struggle to learn or perform.