I went to the Brentalfloss concert back at Too Many Games 2013, and while I don't remember it too well, I know the crowd was really into it, plenty of laughter, bigger fans who had memorized the lyrics shouting them out, tons of solicited and unsolicited engagement with the audience. It wasn't metal concert wild, but it wasn't really supposed to be. I even found some videos people recorded of the event that back up my memories of it
By comparison, the Rex Viper concert feels totally dead despite the audience being way bigger.