The phrase "mess halves" does not have a direct antonym as it is not a commonly used phrase in the English language. However, the word "mess" can have several antonyms such as order, neatness, tidiness, cleanliness, and organization. The antonyms for "halves" can include whole, complete, intact, undivided, and unbroken. When used together, "mess halves" could refer to something that is in disarray and has been divided into two parts. In contrast, the antonyms for "mess halves" might describe something that is well-organized, unbroken and complete.