N.A.T.F.
A dirty insult for someone who talks big but doesn't know the first thing about being a real fan. You're just faking it and probably got here by accident.
"You call yourself a fan? You barely know the main characters!", @FanMaster42 to a guy who watched one episode.
"You're not a fan. You're a spectator with a badge.", @RealFanGang in a group chat.
"You're not a fan, you're just here for the merch.", a guy in a coffee shop arguing with his friend.