The antonyms for the term "most out-of-line" are quite simple to understand. The term means to do something that is inappropriate or unexpected. The antonyms that can be used in place of this phrase would be words like "in-line," "appropriate," or "normal." Actions that are in line with what is expected or considered to be normal are not out-of-line. Similarly, behaviors that are deemed appropriate as per social norms are also antonyms of out-of-line. Hence, one must exercise caution while using such phrases, as it could create confusion and impact the meaning of the sentence.