From my recent experiences in FF XIV, but also seen in other games:
- Plot NPCs who come in after you've done most of the mobs in, help you clean up the last two or so and then states something along the lines of "Good that I came along when I did, right?". Extra points if the NPC in question is a smug asshole. Extra extra points if it's a badly disguised GMPC.
- Main story lines in which you constantly get outclassed by NPCs, despite there being a clear focus on you. I don't mind being one of the background characters, but do make clear if this is the case. If I'm supposed to be a central character, make me feel like it, god damn it.
- Plot-relevant fights with mobs outside of your level range. Don't set me up against something I cannot damage and expect me to look while an NPC kills the way too high level mob.
- Meant to lose fights. I really don't like these, especially because they are so badly implemented most of the time. If it's a proper fight where I feel I may have a chance, but I get killed by the skin of me teeth, it'd be fine, once in a while. However, all of them go like this: I'm fighting a group of mobs, kill all of them, damage a boss while taking no damage myself, the boss hits a certain amount of hp and a cutscene triggers in which I get beaten. Fuck you and your shitty story.
- Random cutscenes showing the bad guys being evil for no reason. Am I playing a bad children's cartoon? No? Then stop making the villains Dark Kantian, for fuck's sake. Unless it's a parody, you're just embarrassing yourself.
- Cross-realm LFG. Yes, it shortens queues, but it also removes any element of consequence for being an asshole in instances, since there's a good chance you're not in a party with anyone from the same server so it's highly likely you'll never see them again.