So Karen is a slang word that people use to describe a specific type of person. They say Karen is a lady who always wants to speak to the manager when something doesn't go her way.
You know when you go to a store or a restaurant and sometimes things don't go perfectly? Maybe they mess up your order or your food is cold. Well, sometimes Karen gets really upset about these things and demands to speak to the manager. That's why people call her Karen.
But it's not just about speaking to the manager. Karen can also be kind of pushy and entitled. She might cut in line or act like she deserves special treatment. Sometimes Karen can be really annoying and you just want her to go away.
So when people say "Don't be a Karen," they're basically saying, "Don't be the type of person who always wants to speak to the manager and acts entitled." It's a way of telling people to be patient, understanding, and kind.