Having been a part of a fandom where the active fans are a fairly tightknit group, I've seen it be applied to that tightknit group slamming someone and his/her work and fannish contributions to the point that there's no one willing to interact with that person for fear of the same treatment. No one's forcing that person to stop being a fan or to stop trying to interact with the fandom at large, but if the fandom has a core group and that core group doesn't want you around? I've seen people be made to feel very unwelcome, and that makes the fandom not so fun anymore, and why stick around if it's not fun anymore?