The phrase "curl one's lip" refers to a facial expression indicating contempt or disgust, typically achieved by lifting the corners of the mouth and pulling back the upper lip. However, there are many antonyms or opposite expressions to this action. For instance, smiling can be an opposite expression showing happiness, pleasure, or approval. Another opposite expression could be pouting, which shows sadness or disappointment. Additionally, frowning or scrunching up one's nose can show a negative feeling or reaction to something, which opposes the curling of lips. Understanding these antonyms can help individuals in effective communication and expression of emotions.