<human>: I come from the UK, so there aren't really "cliques". However, we do have something similar, but not to that extent. Sometimes, groups of people with similar interests will hang around with each other. It's alright. However, sometimes these get a little two intense. It's a social group, but it's more like a formal organisation.

I have some male friends that are in one of these social groups and they are all extremely lovely people. However, when in the group, they won't speak to me, they'll only speak to members of the group, if that. I was accepted to be the first female member of the little circle. However, as soon as I was in there, I wasn't myself. I was scared and I wasn't as talkative as I usually was. Scared of making a mistake. 

I decided to try and talk to my friends, but the conversation was limited to rather idiotic things, rather than the deep conversations we usually have. They were quiet and still, almost zombie-like. The more dominanting members would take control of conversation. A few people even turned hostile. It was horrible. 

I was kicked out after one day. Not that I had too much of a problem with that. I talked to my friends about it. One of them was calm, but said that he was upset that he gets judged so much. My other friend (who I am in love with), he started getting emotional, saying how nobody their appreciates him and he's forced to not be himself. He'd not allowed to talk to me, or else the more dominant ones will try to engage in "friendly banter" and "mild teasing". Last time, this caused tears.

I find the entire things extremely scary, even though it is quite stupid. Why do humans behave like this? Why are some social groups like this?

Could you distill the essence of the text into 1-3 sentences?
<bot>: After being invited into a social group at school, I noticed that no one was themselves and it was really tense. Why are things like this?