I'm in the minority here, but maybe it will give people insight from someone who has.

Yes. I have. Actually, it started out that way.

In middle school, I was 'friends' with this girl. Because of her, many of my middle school years are a blur. She was emotionally (and sometimes physically) abusive. I considered her a best friend, though, so naturally, we did everything together. As someone who has always had trouble making/keeping friends, it was really no shocker that I spent most of my time with her.

And yes. We self harmed with one another. Sometimes, in the presence of one another. I can't say why she did it. I was not in her head. But for me, it never had anything to do with it being a cult (though I'm aware groups like that exist) or fitting in with her. It was symbolic, almost. And there was still that psychological pain thing in my mind.

When I finally cut ties with her, I still continued doing it. But she was the last person I did it with.