No idea.
I'm the polar opposite. I'm in my seat 20 mins early watching the warm up/build up and never get my fanny in a twist about my neighbor arriving 5/10/15/20 minutes late or leaving early.
They might be having a chat in the bar, eating a pie in the foyer or taking a long $hit. Who knows...
People always find something to moan about.
The way I see it, they've paid for their seat, they can do pretty much what they want with it but stand on it.