Name changed for this one.
Friend A, let's call her Dierdre, was annoyed with friend B, let's call her Helen, for something she was going to do, which wasn't really anything to do with Diedre, but Diedre felt it was.
Diedre snitched on Helen to mutual place, where we all know each other from, for what Helen was going to do, and Helen saw her doing it. Helen got into trouble. Before this happened Diedre started a pile on towards Helen in group whatsapp and lots of people jumped on after Diedre started pushing Helen to not do the thing she wanted to do.
It wasn't a bad thing Helen was doing, but it made other people feel uncomfortable. Think a small rule broken- maybe as trivial as jumping over the train station toilet turnstiles when you're completely out of change, and desperate for the loo, and everyone tutting at you. But because of Diedre snitching to place which took rule very seriously, Helen ended up humiliated. Helen was really upset by whole thing. I'm quite friendly with everyone in group setting, as is Diedre, but Helen is quite nervous and withdrawn.
I am friendly with both Helen and Diedre, and know that Helen is very vulnerable for multiple reasons. I spoke up for Helen in the group after the pile-on, and said it shouldn't have gone that far, and I probably have to face Diedre soon, in group setting. Diedre doesn't know that I know that she snitched, and doesn't know that Helen knows, but is usually quite honest about what she has done, as she has complained about other people before. But she knows I spoke up about Helen's treatment by her and others in whatsapp group. Problem is, she doesn't know the consequences of what happened to Helen when she got into trouble for it.
So sorry if this is complicated, but even one detail would be completely outing!