Forbidden banished exiles. Especially in MMORPGs, I've found that the most common overall in-setting guild theme is "we don't belong in the society that this setting established." It's not just in MMORPGs, of course. It's often a crutch (or training wheels, if I'm being generous) for some roleplayers to participate by not participating. I'm not saying that a character (or a player for that matter) has to bend the knee to Lord So-And-So, but it's kind of hard to find plot excuses for the the forbidden banished exile to even be in the same picture, let alone get the quest to do the thing.
Plot armor dependents. Yes, it's quite likely that if I'm running the game and telling the story that I won't have the guards kill a player character on sight even if they do something exceptionally stupid just to see what happens, like stabbing a random citizen. Those kind of players don't tend to last long if their only contribution is "try to knock down the props just to see what happens on set."
People that directly lift an established character in well known fiction, often just changing the spelling, and often not even trying to resemble or act like that character. In an older MUD, I recall a "Frrodoh Bhaginz" that was a Half-Ogre hunter. Again, it didn't ruin the game, but it was annoying. I admit it can sometimes be a red flag warning, and a helpful one, if the lifted name is from chud fiction, like if they have "Rahl" in their name. It can show me what to expect, either in a tabletop group or in a MMORPG guild.
Railroading is often described as forcing the party through a story, but the reality is that it's more about robbing players of agency. RPGs are always bounded in some way, but players get to exercise agency within those boundaries, and that's where the gameplay emerges. Sometimes the outcome of a situation is set (Get in the fucking robot, Shinji), but the way they get to that outcome can be extremely enjoyable. Do you go through the window or the front door? Do you fight or sneak? Do you try charm or intimidation? Railroading is when the GM takes those decisions away from the player, which is anti-fun.