People are insecure. The only reason they could have to be mean to somebody would be to prop themselves up and make them feel better about their own situation. Accept that there are mean people in the world. Unfortunately, not everyone you meet or interact with is going to like you or be nice to you. But that doesn't mean you shouldn't put yourself out there! In fact, being aware of the fact that there are mean, careless, or bitter people out in the world will make you appreciate all of the good people in your life even more. If someone is just outright rude to you for no reason, then you need to learn to accept that this is a result of that person's insecurities and personal issues, and not because of something you did. Remind yourself that it takes all kinds of people to make the world. Not everyone is going to be your best friend, but that also doesn't mean everyone wants to be your worst enemy.