We all have insecurities.

Some are insecure about the way that they look, personality traits, or social status.  What sucks is when someone allows their insecurities to foam from their mouth to bring others down in order to lift themselves up.

This tactic or strategy is caused from the inferiority complex.  The idea is that if you feel awful about yourself, you say and do things to make others feel even worse, in hopes that you make yourself feel better.  

In reality, you crush the people around you, making them want to scatter and hide, which reaffirms the negative things you believed about yourself in the first place.