Au fait is a French term commonly used in the English language to describe someone who is well-informed, knowledgeable or up-to-date with a particular topic or subject. The word has a positive connotation and represents a state of competence and proficiency.
Some antonyms for au fait include: clueless, inexperienced, ignorant, unskilled, and uninformed. These words describe someone who lacks knowledge, skills or experience in a specific field, and are the opposite of someone who is au fait.
It is important to note that antonyms are not always negative. Being ignorant or inexperienced can be an opportunity to learn and gain experience which can lead to becoming au fait in a particular area.