Having been in this situation before (years ago when I sat next to an extra-loud popcorn eater at a movie theater), I knew this about myself:  once I complained, even if the offender stopped the offending conduct, I would be so self-conscious about having made a fuss that I would not have enjoyed the rest of the performance.  So I chose the path of least resistance, moved to an empty seat several rows back and salvaged the rest of the concert.  Cowardly, yes, but at least give me points for self-awareness!