Why do people make fun of others?

People make fun of others because the are insecure or have a need to feel superior to others. It can include jealousy, like if a fat girl is making fun of you, they are jealous that you have the body they want. Others simply cannot accept differences.

There is also a pack mentality at work. Animals that hunt in packs look for the weakest among their prey because they are the easiest to attack. Bullying works much the same way. The aggressors often choose those they perceive as the weakest. So if someone else is insecure, has a poor self-esteem, doesn't seem to fit in, seems different, and seems oblivious to the world, they would be the first target.

Sometimes people bully others because they hate something in themselves that others remind them of, or because the other person is doing something really bold that they secretly want to do themselves. So they bully and ridicule others who are most like them to keep others from suspecting they are different, or because they are mad that another person can openly be what they can only dream to be.
People do that because they are just big jerks that obviously are losers with boring lives and are seeking attention, which is not good. They may be jealous of you or see you as weak. Or they could hate themselves, be covering for a weakness in themselves, or believe that bullying prevents them from being bullied. So if anyone makes fun of you or bullies you to your face here are the list of things to do below.

1. Be polite and say please stop bothering. (If they don't stop proceed to step 2.)

2. Try to ignore them. (If they don't stop proceed to step 3)

3. Tell an adult. (If does not work proceed to step 4)

4. If they keep keep touching you and hitting you, proceed to step 5.

5. Use whatever reasonable self-defense.
They are either jealous of them, or they just have absolutely nothing else to do.