The term "most crackerjack" refers to someone or something that is exceptionally skilled or proficient. Its antonyms would be "incompetent," "inept," "amateurish," "clumsy," or "unskilled." These terms describe individuals or objects that lack the ability or expertise to perform a task effectively. An incompetent person may have a poor understanding of the job's requirements, while an amateurish action may result in a disappointing outcome. On the other hand, a skilled, proficient person or thing may be labeled "proficient," "expert," "adept," or "masterful." The antonyms of "most crackerjack" highlight the contrast between exceptional and lackluster performance.