The phrase "know backwards forwards" means having a thorough understanding of a subject or topic. Antonyms for this phrase may include "ignorant," lacking knowledge or awareness, or "clueless," having little to no understanding of a particular matter. Other antonyms could include "naive," showing lack of experience or judgment, or "uninformed," not having enough information or knowledge to make a proper decision. Alternatively, "unfamiliar," indicating a lack of knowledge or understanding for a particular subject, could also be an antonym for "know backwards forwards." Overall, there are many words that could serve as antonyms for "know backwards forwards," all conveying a sense of not being knowledgeable or well-informed.