Daniel Wakin says that while the opera world is full of outsize egos, Roberto Alagna’s onstage tantrum this week is one for the ages. Moreover, Alagna’s subsequent ban from the La Scala stage affects more than just a week’s worth of ticketbuyers in Milan. “The cancellations will also probably trouble executives at Decca Classics, which was making a DVD of the production. No decision has been made about whether to issue it.” UPDATE: Here’s the video of the walkout