Suffer not the furry to live

This story has a very similar plot to Fur Heresy: A group of 40k fans plays a role-playing game, upon discovering that one of the participants (in both cases formerly a friend of the narrator) has created a Mary Sue furry race and retconned it to be secretly responsible for everything plot-relevant in the past. Players act in-character ("it's what my character would do" is not always bad, and it is the perfect weapon against "magical realm" DMs who act as if NPCs wouldn't react the same way either), and by the time the DM realizes the player's plan to commit furrycide, it's too late to prevent it without obvious retconning, so the DM becomes unreasonably angry before shutting down the game and gathering a pro-furry clique.