Other stuff aside from the biggest one that I mentioned way back (incessant screamers):
-People who are too glued to their phones to notice that the line has moved and then shoot you the worst "go **** your mother" looks imaginable when you politely remind them that they're holding up the line. There is more to life than posting stupid memes on Instagram or creeping on teenage girls on Snapchat, goddammit.
-Groups who abuse single-rider lines, especially if they get abusive when the attendants call them out on it. This is how single-rider lines get taken away, dickheads.
-People who leave unholy messes in restrooms. Dogma was a fictional work and there's really no need to try and recreate the Golgothan and you people are just disgusting in general.
-People blaring terrible music on their phones in line. Yeah, I'm just as sick of Taylor Swift and Katy Perry playing in the background as you probably are, but trying to drown them out with Chief Keef or Five Finger Death Punch only makes it worse.
-PDAs. Absolutely no one asked to watch you and your trashy girlfriend simulate mutual facial cannibalism while you shove your hands down each others' pants. Seriously, DON'T.