"Neat as pin" is a commonly used phrase to describe clean and orderly surroundings. However, there are various antonyms for this phrase that describe the opposite of neatness. "Messy" and "cluttered" are two words that immediately come to mind. A space that is disorganized and untidy can be described as chaotic or unkempt. Another word that can be used to describe messiness is "disheveled," which implies a lack of care or attention. Additionally, "untidy," "slipshod" and "sloppy" are all good antonyms for "neat as a pin" that describe a space that is not well-organized, clean or orderly.