1. To encourage someone to be brave or tough. This is the most common meaning. It's a way of telling someone to suck it up, be strong, and not let something get to them.
Example: "You're feeling a little down about the interview? Don't worry, it's your upper lip!"
2. To suggest someone is being arrogant or conceited. In this case, the phrase is a bit more sarcastic and means that the person is being overly confident and needs to be humbled.
Example: "He's been bragging about his new car all night. Someone needs to tell him it's his upper lip!"
3. To refer to an actual physical feature. This is a much less common usage and would likely only be used in a specific context related to the upper lip.
Example: "The doctor said it's a problem with my upper lip."
It's important to consider the context in which the phrase is used to determine the intended meaning.
Let me know if you have more context and I can help you interpret it better!