why bullies have so fun to bully people?

Teenagers feel weak, so they pick on kids weaker then them so they feel as if they have some power. I think if you want to improve your self esteem there are other ways, besides bulling

It gives them a sense of power over another person and it goes to their head, the best thing you can do is stand up for your self even if you get a beating, and show them that you are in charge of your life and not them. If they try to beat you fight back! Show them you will not let them run over you without a fight, and if theirs more then one rally anyone else who is willing to stand up for their rights.

they are jealous of my pet unicorn

Because they like to be telled on. Plus they don't know what the meaning of life.

Cause they really don't have anything else to do really, cause they don't have hobbies to focus on or anything, cause they have nothing important to do in their life, and they think their better then everybody.