Notice how often a friend tries to embarrass you or make you look bad in front of anyone or everyone, especially after you've told, asked, or begged them to stop. This can be a major sign that the person does not care for you as a friend but rather as a source of entertainment, at your expense, of course.
Observe if the "friend" is mean to you or makes fun of you all the time. A mean friend may try to take advantage of you or possibly push you around. Keep in mind that some friends make fun of you in a joking way, while others do it to lower your self-esteem. Realize what they are doing, and find someone else who appreciates you.
Notice how often a friend breaks promises that they make to you. Maybe your friend calls you up to see a movie, but then cancels your plans at the last minute, or even worse only a minute or two after making it. This can be a major sign that the person does not want your friendship but only your companionship, and only when they can get nobody better to fill that void.
Notice how often they belittle your accomplishments. If you write a superb piece of fiction they will accuse you of plagiarizing it from another source. Sometimes they will praise your work to your face, but you may discover they are making fun of it behind your back. Being two-faced is not a sign of a real friend.
Notice how often they ignore you: ignore what you say, ignore your presence, fail to introduce you when they're making introductions, they offer something to someone nearby but not to you, etc.
Notice how often a friend chews you out for making mistakes, or chews you out for bringing their mistakes to their attention but chews you out for making even little mistakes. Some people want to surround themselves with perfectly-behaving people so that they will be perceived as being better than they actually are.
If they do not respect what you like as well as dislike. True friends respect the things that you like so, they would not want to change your field of interest.
Real friends respect another friends' moral values. If you have very high moral values, then your friends should either share the same values or respect them.
Real friends love you just the way you are. If they are trying to change you in a way that makes them accept you, then don't waste your time on them.
Source: WikiHow