Forgetting to turn off a phone is annoying but something I can understand and have some patience for. If a concert has 500 people and and you forget just 0.2% of the time, then there will be at least one who will accidentally forget. It sucks but it happens, and most of the time the phone owner is just as annoyed as anyone else.

Standing around chatting is something else entirely. Standing around chatting after being told it's not appreciated is something I can only accurately describe in words I'll omit here for politeness.