What do I do when people are not nice to a certain person?

you should stand up to the person being bullied or abused, because that involves courage; and the people picking on that person are nothing more than cowards who need to start learning that it's not about them, but it's about helping each other up, and if you can't do that, you will suffer the consequences of contributing to all that is wrong in society.

a look of disgust just may say more than words

flying kick them in the face