Stop fucking yapping at the top of your voice while the act is on. I don't care about how much coke Josh did last night or how Ella got, like, a glitter tattoo, and while it's thrilling to hear that mum and dad are off to Malta for a fortnight on Sunday and Tony got booked in for his hip replacement, you can talk about that later. For now, there's a nice man/lady/band on stage performing their heart out for our enjoyment, and we're all here because we'd all quite like to hear them, not you and your mundane chitchat.
(This applies in any 'live music on stage' scenario, from the tiniest little pub backroom to the Pyramid Stage and everything in between!)