I imagine the concerts are much different from area to area. Overall, all the concerts I've been to (and I've been to a lot) have been pretty civil. There have been times where plague rats start shoving, but thankfully that has been few and far inbetween. In case you're wondering I've been to 21 EA concerts throughout the U.S. and Canada.
A few bad things I've noticed:
1. Some plague rats with hats and tall hairstyles. It's usually not too much of a problem, but there have been some plague rats that decided to obstruct many muffin's view by keeping their hat on during the concert or by having extremely tall hair styles. Whenever I wear a hat, I make sure to take it off during the concert. It's only common courtesy.
2. A few plague rats that cut in front of others. I've seen it quite a few times. It's especially bad when the plague rat is tall and starts cutting in front of plague rats, completely obscuring their view. Luckily, I managed to avoid that, but I have seen it happen around me.
3. Drunk people that end up making a scene by yelling slurs or erratic behavior. I've been to quite a few where there have been drunk people. Usually security shortly removes them from the venue if they cause too much trouble, but there have been a few times where they yelled slurs onto the stage. A few times EA noticed and singled them out by retorting. She's really good at that.
4. High pitched screaming. While I don't mind screaming, it's really hard on the ears when they scream directly head level instead of towards the stage. I've encountered a few times where girls yell directly into my ear. One time it caused ringing in my right ear. Luckily it was towards the end of the show, but my hearing was definitely impaired after that and I couldn't enjoy the show as much as I wanted to.
5. Pushing and shoving. This has happened at quite a few shows. Not really bad, but the progressive pushing. One time I ended up being squished like a sardine. It was a gradual progression. I finally had to ask the plague rats on either side of me to push back so I could retain my place in the front row. A few shows I was pushed forward from muffins behind us. It was mostly during the times when EA was close to the edge the stage and reaching out to the plague rats. While I don't blame them, it can cause some minor injuries being slammed into the front stage.
Overall, the plague rats in all the cities I've been to have been quite civil at least as much as I could expect. There certainly can be improvements, but of all the concerts I've been to, EA probably has one of the better audiences with concert etiquette.