Most of mine have already been said, but I'll put in my two cents!! :)
-When a flyer hits the ground; inexcusable... this goes for practices too, but especially at competition! If it's going on the floor, I shouldn't have to fight the urge to run onto the mat and spot your stunt for you...
-When flexibility isn't really flexibility; if you're going to show me a scale that like bends at a right angle or an arabesque that's not perpendicular to the floor, keep stretching... don't put it in a stunt
-People who save seats at venues...
-Teams that don't clap for other teams at awards
-Teams who scream and jump up and down when they've realized they've won after second place is announced; let everyone have their moment... you'll get yours in about 45 seconds...
-ANYONE who gives up... it's only 2.5 minutes; I totally get being frustrated and disappointed if a stunt doesn't hit or your tumbling pass isn't perfect, but don't just sulk on the floor or hold your flyer in smush and look around confused... every second is an opportunity to make up points!
-Flyers that look terrified... love what you do... trust your bases... I hate watching someone in the air who looks like they're about to cry! :(
-Teammates that don't support each other... even if the routine doesn't go perfectly, it's only one routine and you still have to see each other in the gym at the next practice! Don't come off the floor and start blaming!
-Skills that are obviously just put in because an athlete can "do" it, but have no technique: bent arms/legs in back handsprings, crossed legs and bad angles on fulls/doubles, feet that come apart in smush, etc.