The antonyms for the word "most overconscientious" are "careless," "negligent," "indifferent," "unconcerned," and "reckless." Those who are careless are not mindful of details and do not exercise caution. Negligent individuals fail to provide proper attention or care, while indifferent ones are disinterested or apathetic. Those who are unconcerned do not care about the outcome or consequences, and reckless people act without thinking of the consequences. Thus, these antonyms describe individuals who lack diligence, responsibility, and carefulness, and do not possess the qualities of being overconscientious.