Someone stuck-up acts like they're better than everyone else and treats others as though they're not worth their time. A stuck-up classmate might refuse to sit with certain kids at lunch, roll their eyes when someone asks a question, or brag constantly about their possessions or achievements while putting others down.

Stuck-up people often come across as snobbish or conceited. They might ignore you in the hallway, make you feel small for not having the right clothes or hobbies, or act bored when you're talking. The phrase captures how these people seem to have their noses stuck up in the air, as if they're literally looking down on everyone around them.

Being stuck-up is different from being proud of real accomplishments or having high standards for yourself. A student who works hard and feels good about their grades isn't stuck-up. But if that same student starts acting superior to classmates who struggle more, or refuses to help others because they're “too smart” for that, then they're being stuck-up.

Interestingly, people who act stuck-up are sometimes insecure, trying to make themselves feel important by making others feel less important. Acting that way can quickly damage friendships and respect.