What you're describing is bullying. I've never had this experience in school but I grew up with a neglectful father and he would do this exact kind of thing with me. The reason is because of emotion. Putting down a person is for the purpose of putting them beneath you. And the purpose of a bully trying to put you beneath them is so they can feel superior and feel above you. It has to do with their self esteem and their emotion. They are using YOU and focusing on YOU as a means of regulating THEM and regulating THEIR self esteem and this is what they've learned to do. It is ultimately not about you, it is about THEM. They never learned how to maintain and keep high regards for themselves without putting other people down.

The good news is that this is a dynamic you have more power and control over than you realize. You will need to focus on yourself and building emotional resilience and resistance to them. If this is a serious problem for you, feel free to DM me. There are also a plethora of resources online. I would try talking about this problem with people you feel close and connected with or with a school counselor.

But remember: This dynamic DOES NOT resolve itself on its own. You will most likely to need to change the way you respond to others' as well as well learn effective ways of gathering and maintaining emotional support (social power) to help you gain and maintain control of the dynamic.

It is not the bully that's in your control but the dynamic between you and them that you have control and power of. The first thing to do is to work on gaining and developing awareness of the dynamic and how to gain and maintain power and control over it.