why do people make fun of other people?

i always wondered since i was a kid. i was always getting made fun of by people when i was little...particially because i was little, smaller than everyone else by alot. i was really really skinny and everyone thought i was wierd so they all made fun of me.
its annoying and upsetting when people poke fun at you just for being you...i used to try to be like everyone esle when i was little hoping that it would stop but it didnt. i never really got it. i didnt make fun of people and i tried hard to be nice to everyone but nothing helped, but i couldnt get it out of me to be mean to them so it kept going. i was also only black person in my school for a little while and when i got to a school with black people, i acted different than all of them and then they made fun of me too. even when i got a group of friends i was still always the odd one out, but at least they liked me for it. it just never felt like i really fit in anywhere. i did like going to art club though, all of the people there (probably because they're artists) accept everyone as soon as they come in and make them feel at home. unfortunately i had to stop going because no one could take me home.
i kind of make fun of people sometimes now but i can stop myself. i dont think its very nice :/ i always say sorry to them even if they dont know i did it, because you might not know what they're going through or what goes through their head and it might actually be hurting them and i understand that which is why i always feel bad.
when people make fun of someone else, the person gets self concious and that's never really a good thing, bcoz when u make fun of someone they might not have noticed what you said about them until you said it and when it rubs them in the face they try to remove and when they cant they feel bad about themself.
maybe ppl do it to make themself feel better...maybe they just like to see people feel bad :/ i dont really know but even something as little as being poked fun at can change someones whole life. because when i really think about it my entire childhood would have been different if people hadnt been mean to me and that means i would probably been different as a teenager and a young adult right now. if you really think about it...