ONE: Talking on your phone.
ONE: Talking on your phone. Maybe your mate’s outside, maybe he can’t get in, most likely you don’t have a clue where he is because You Can’t Hear Him, even shouting "I can’t hear you!" won’t enable you to hear him, but it will annoy the hell out of the people standing next to you. The reason you can’t hear him is because you’re in a gig and there’s music going on. That’s what those people around you want to listen to, not you.
Back in the day, there used to be an expectation that you’d turn your phone off during cultural events like films or gigs. Well no-one does that anymore, indeed far from turning their phones off, people are more likely to be waving them around doing things with them.
On these occasions, pretty much anything you do with your phone when you are supposed to be communing with music will annoy someone.
Yes, the mobile-in-gig etiquette is different depending on whether it’s an intimate acoustic set with a singer/songwriter or a stadium rock-metal gig with speakers the size of Mount Everest. But still, some things are just not acceptable.