The ones I find annoying are mobile phones (cell phones).

Those of us old enough will remember how certain songs used to produce a forest of matches, or cigarette lighters, waved above heads.

Now it's little glowing screens, as people all try to film the performance on their phones, then sit hunched over them as they send the film to all their mates.

I don't know why it's distracting when other people aren't paying attention at a concert they've paid money to attend. But it is.