fake fans

 You can tell who the real fans are at metal concerts because they are able to match their headbanging with the seemingly sudden time signature or tempo changes.  "Look at that idiot, he was still headbanging at 120bpm two beats into the new measure when the tempo had clearly changed to 180bpm!  Any REAL fan would know that the tempo changes after he sings 'eat my bloody corpse'!" they might think to themselves self-righteously, as a snotty little smirk grows across their faces.  The pop equivalent to this is catching someone awkwardly trying to mouth the words to a song they don't know, whilst visible beads of sweat form at their crown.   "Please god!" they implore "Don't let Britney notice that I don't know the lyrics of her song!  Oh WHY did I have to elbow my way up to the front??  WHY!?"