One pet peeve that I encountered at Consonance was somebody banging away on a laptop keyboard in the middle of a concert. It was annoying. Go out in the hall. The fact that it was more than one person? *sigh* Get a quieter keyboard or perhaps don't type as hard?
The people who were whispering entire paragraphs - you're not as quiet as you think.
Ditto with the person on the phone and the group in the back who had a very LOUD conversation going on. A capella song doesn't work real well against loud talking. GRRRRRRRRRRR... This particular group has been warned more than once. The door's right there!
This isn't just Con behavior. It's any kind of theatre too. (don't get me started on the bright light of phones in a darkened theatre)
Common sense? Common courtesy?