The phrase "most simpatico" refers to someone or something that is very likable, agreeable or compatible. The antonyms for this phrase could be "unfriendly," "incompatible," or "antipathetic." Instead of being harmonious and sympathetic, someone who is "unfriendly" could be cold, aloof, or disagreeable. On the other hand, something that is "incompatible" may be unsuitable, inappropriate, or inconsistent. Lastly, "antipathetic" means having a strong dislike or hatred towards someone or something. Thus, while most simpatico relates to positive interaction, its antonyms relate to negative ones.