For me it's arrogant players that know little but think you are wrong when you are doing something they don't understand.
But also and not limited to:
Surgeons or even medics who claim ORs and keep the tools always on them.
The CMOs who don't care about it or any other similar problems.
Janitors who keep re-cleaning the clean floors of the main hallway just to have fun.
Anyone who ask you how to play and don't give a shit about the wiki links you sent by LOOC.
When a security officer see that you are standing still and stuns you without a word, on green, because you are needed at the brig to answer some questions or some other reason without any evidence.
Players who commit suicide at roundstart for absolutely no RP reason (wait, is that ahelpeable?).
People who go to long term storage at 12:15 without a word. Specially chemist, cargo techs, chefs or other important roles where they are really needed.
Medbay patients that tell you how to cure them even if you are administrating a more suitable cure. They insists that they know better and get mad.
New chemist players making empty pills/patches and refusing to learn when you try to help.
Cargo techs who order medical supplies and weapons at roundstart for themselves just in case things get bad, and reordering the crates after the QM cancelled the first ones.
People who left food plates with only one bit left. Then it looks like you are eating a lot when you are actually taking just the last bit of each plate and then everybody looks bad at you and the chef now hates you.
People reporting cultist like it is a normal thing on the station because saw someone whispering twice.
Security staff who forces you to take holy water for any minor crime not related to vampirism when there are confirmed vampires.
Players who fell on a wet floor. You help them get up. They walk towards you, making you to fall on the wet floor they were. They walk away, nobody helps you.
Stealing the piano from the bar.
Stopping the really cool song you just started at the piano just to play moonlight sonata from the wiki.
Electric guitars.
Bartender who doesn't tend to the bar.
Plasmamen who die and need cloning. Just ban them for dying.
Someone stealing your arcade tickets.