For small shows I hate when people talk the whole time, its like they came to have their own party and dont even care about the person on stage.  I also get annoyed by clappers.  The people who clap during every single song and normally not even on the beat, especially if they feel the need to stand so close to you and do it in your ear. 

When people wait in line all day and people push and pull to get up front is beyond annoying.  Or when you are up front and an artist comes towards the end of the stage and everyone reaches and pushes you into the stage/barricade. 

And the biggest thing that bugs me is when people throw stuff on stage or try and grab hold of the artist and not let go.  I feel bad for them, just let them do their thing.