Why are people sometimes mean to people they like?

Because it’s a way of getting their attention and interacting with them without the risk of embarrassment, rejection, or heartbreak.

It is called being “tsundere”.

It depends.

Sometimes it’s teasing, which can be for affectionate reasons rather than hostile ones. Such reasons are sometimes partly sub-conscious. Children in particular will tease parents because they are curious, like to see the reaction and/or get an interaction, attention, and/or amusement in a loving way, and I think as a subconscious way to offer mirroring that brings attention to the parent’s own organization, often of ways that can benefit from attention.

It’s a superiority complex thing. And a competition thing.

I don’t think it is tsundere what the OP is referring to, but maybe. I think of tsundere as slow to warm up to someone. Being very cold initially.

I think the mean girls thing sometimes is being mean after there is already a relationship sometimes. I caught myself being short with a friend the other day. She can be very controlling. I can’t emphasize enough how controlling she can be. Anyway, a few days ago she was asking me to go to one thing and another, and telling me her whole schedule for the next few days, and it started to feel manipulative and like pressure. When I responded I couldn’t come to several of the things I feel I had a tone that was mean. I think her intention is good, but it is overwhelming. I think my sharp retort was trying to get my power back, but really I did not have to respond that way.

She also influenced me to make a decision I regret, but I don’t blame her for it, there were jellies also that pushed me to the same decision. In the end it was my own decision, but when she says anything that takes me back to that situation, I’m on edge, which might come off as mean. I hope not. I really try not to be, but I am quick to tell her where she is wrong when it comes to things related to that particular situation.

Sometimes I think it is about a power struggle, or even maybe to feel superior over the other person. In fact, I would say mean girls mostly is trying to put someone down so you feel superior. I’m not one to be competitive in friendships or with coworkers, I am very team oriented, and often I am the manager, so I am not competing with my staff, but rather trying to help them shine so I shine. My SIL is a classic mean girl, putting others down, or giving a look of disapproval.

So, maybe always about power and control, but in some instances it is trying to protect oneself, and in other cases it is power over the other person.

They are emotionally inadequate.