Call me old fashioned, but back in my day, we would stay still and then clap at the end of a song to show our appreciation for the band. If the performance was particularly well done, I would occasionally shout a "Whoo!" to express my admiration and respect for the job they were doing.
I saw Manchester Orchestra at a street fair on Saturday and it was the roughest show I've been to in a long time. It was an array of shitty teens/early 20 somethings who just wanted to be rough with strangers. I saw 2 kids almost get their asses beat by older CLEARLY drunk folks, including one woman and her husband. It pissed me off to no end, but it was essentially a free show, so I feel like it wouldn't have been like that if it were an actual venue.
Or maybe I'm just old.