The phrase "be on the warpath" is typically used to describe someone who is angry or agitated and ready to confront or attack someone or something. Its antonyms would include being calm, serene, peaceful, or tranquil. These are all opposite states of being that denote a sense of relaxation, composure, and tranquility. An individual in such a state would not be interested in attacking, confronting, or inciting conflict. Overall, using antonyms for "be on the warpath" would convey a sense of calmness, reflection, and restraint that can help diffuse aggressive or confrontational situations.