The phrase "most gentlemanlike" implies someone who embodies qualities such as grace, chivalry, and respectfulness. The antonyms for this phrase could include words such as boorish, uncultured, uncivil, and impolite. These words describe someone who lacks the basic manners and civilities associated with being a gentleman. Other antonyms could include unrefined, barbarous, crude, and discourteous. These words describe someone who is lacking in elegance, sophistication, and class, which are key traits of true gentlemanliness. In short, the antonyms for "most gentlemanlike" describe individuals who are the exact opposite of what it means to be a true gentleman.