@lemmy_user_838586 Reddit used to have a left wing political sub called ChapoTraphouse. After it got banned its users all moved to their own fediverse site, Hexbear. It has its own site culture, slang, name-calling, and memes.
It has been defederated from quite a lot of instances.
It was not federated for a long period of time. Part of its - culture involves what it calls "dunking" on people its users disagree with politically, which as far as I can see is a compendium with snark at one end and bullying at the other.
When Hexbear federated, its users were "excited to dunk" on people again. Their copious use of visual memes, including a picture of pig testicles covered in excrement, stretched threads. They are also a big community, which means when they pile into a thread it looks like brigading.
The situation wasn't helped by large numbers of Hexbear users coming into threads where other instances tried to discuss what to do about issues around federating with Hexbear. As larger instances defederated them, they became disproportionately drawn to small instances that remained, which added to the brigading effect and led to more defederations.