Doors open at 7. Opening band starts at 8. The headliner starts at 9-ish. When do you show up? Obvs this is dependent on who is playing, but let's go for averages. Your tendencies. What's your gut reaction?

I was at a show last night and the person next to me was singing along to every word of every song. While that in and of itself is not a crime (maybe a bit of moderation mighta been nice?), this person also couldn’t have found the right key with GPS. Is there anything at a concert that absolutely drives you nuts when someone near you does it?