One of my symphony pet peeves is those in the audience who start to applaud before the performance finishes! It just bugs me in recordings when you hear that lone eager clapper jumping in and abrupt the ending of the piece.

My rule of thumb: watch the conductor. When the conductor relaxes, that is when the performance is truly done. Let the musicians hold the final phrase and allow the moment to sink in! It's part of the experience!

Another are those who cough with their mouth open. Why?!