If someone flatters you, they praise you in an exaggerated way that is not sincere, because they want to please you or to persuade you to do something.

If you flatter yourself that something good is the case, you believe that it is true, although others may disagree. If someone says to you 'you're flattering yourself' or 'don't flatter yourself', they mean that they disagree with your good opinion of yourself.

If something flatters you, it makes you appear more attractive.