The phrase "curl one's lip" refers to the action of showing disgust or distaste by raising the corners of the mouth and exposing the teeth. Antonyms for this expression might include phrases that describe opposite facial gestures, such as smiling broadly, grinning from ear to ear, or laughing heartily. Other antonyms could refer to expressions that convey a neutral or positive emotional state, such as maintaining a poker face, keeping a straight face, or showing a gentle, sincere smile. While "curl one's lip" implies a negative reaction, antonyms might focus on more positive or ambiguous facial expressions to convey a different mood or tone.