Ryan is right. People who don't have a positive self-image try to bring other people down to either feel better about themselves or to try to make other people look upon them better than the person they are belittling. And while it might be a coping mechanism, it's not the right thing to do. The person you're doing this to is not going to feel very good about you if you're the one doing it, and other people are also going to think less of you for trying to make someone look less in the eyes of others. If you have a problem, you need to fix it. Seek professional counseling if you must. Otherwise, find out what it is you don't like about yourself and try to change it if you can. There's a myriad of self-help books available on just about every subject. If you need to lose weight, do so. If it's something about your body that you can't change, then consider plastic surgery. If that's not an option, then learn to accept it and yourself. But ridiculing others is never a solution.
Yes, people who do this often think very low of themselves. They are trying to play off as if they are cool and above others so that people will like them. The truth of the matter is, if they didn't have any friends around to parade around with them while they put others down I guarantee they wouldn't be doing it.
I know it's hard to deal with but you must try and keep your head held high. When they speak do not react or do the opposite and simply tell them you do not want to hear anything negative come out of their mouth about you again. I'm not sure how bad it has gotten or if it is classmates or family members. Don't allow them to take away your self worth, your better then that.
People who put others down are very insecure themselves and usually they do not have the guts to do the things which they critisize others about. Ignore people who put you down and focus on those who don't. Also make sure that you support and encourage those around you. Eventually the people who put you down will seem silly.
What pretty much everyone else said is true; I just want to add that it also becomes a learned habit. One doesn't have to develop ideal self-esteem in order to unlearn that habit and begin treating people better. In fact, that can be part of the path to self-esteem.
probably because deep down that person is insecure. Remember though not 'everyone' is like that, there are nice people out there:)
People that do this more than often than not have low self esteem themselves. They act this way as a coping or defense mechanism.
An effort to make themselves look important.....flawed character