Chillax everybody. :) I was there, and the booing was NOT for the band, as the OP of the booing incident said. Chris mentioned that they were nearly done with the show, and said something like "then you won't have to see us for another 10 years." THAT'S when the audience "booed".
And Chris didn't seem irritated about it to me. Maybe a bit surprised that they responded to the comment with booing instead of maybe like "awww" or something. He said "Don't boo!" and laughed a little.
The crowd was a bit dead at times, though. Even though some articles have said that there were a lot of teens and twenty-somethings, there were a lot of older people there too, and parents with their children. A lot of them seemed like they weren't really excited to be there in the first place.