Hi there. I’m that quiet person you didn’t notice, or the person singing along with the song, or maybe I’m dancing to the music. All these things are appropriate at a concert. If you are doing anything else… you’re doing it wrong. 

If you have a friend that wants to take a picture or two during a concert… cool… if they want to record the whole song… take their phone away. There are people venues pay to take real pictures and video… go to a site, or look up the band… hit save… it’s a way better version of whatever shitty picture/video you were trying to take. You can post that on whatever.
You won’t watch it later, it wont sound good, none of your friends care.
 
If you like to talk, great. Just don’t talk during a concert. Now is not a time to catch up with your friends. If you like the person performing, imagine for a second how much they hate people like you… they worked all their lives, wrote this meaningful shit and you show up and add your noise. 
 
If you have a friend like this… bring a rag…. shove it in their mouth and whisper,”Listen….. shh… listen
 
That’s it. Don’t record the whole show, don’t ruin the sound, don’t distract people. If you’re friends with these people… bring a rag, take their phones, or just don’t bring them.