Stock standard common courtesy.
If you want to talk to your best mate sitting next to you in the auditorium, just remember we can all hear you. You might want to continue your private chat outside so we can all hear the speaker on the stage. This one also applies to the theatre, movie and live but will save that for another spray.
‘the grammar police got him
split his infinitive open,
removed his colon
and left him lying commatose
the next day he was pronouned dead