What aspect of gameplay is your biggest pet peeve?

Escort missions. They usually involve useless characters who run around and die, failing the mission, at the first sign of trouble. Also time limits in games when they are not needed.

Following missions in open-world games. Not the the ones that you have to stalk someone, I mean those kind of missions that you get the objective while following a friendly character.

Just can't maintain speed and listen/read subtitles at the same time.

ive said it before and ill say it again fmv's that dont allow you to skip them

Boss battles
Unlocks

Escort quests and tutorials that walk you through the most basic concepts of the game at such length that the rest of the game seems brief, which you of course cannot skip.

Fetch missions for shit rewards.

Unnecessary micromanagement and pointless motion control.

I guess Saints Row 3 made me at least a little bit pissed off at aim assist that I can't turn off. I can follow enemy movement without you helping me, game, so quit it! It gets in the way of normal aiming more often than not.

long cutscenes, invisible walls, repetition/griding, (forced) backtracking just to extend gametime

CHECKPOINT SYSTEM!! How I feel like when I find out the game has it

pointless grinding and shitty Quick time events.

Besides games being repetitive, I hate playing with people online who are vulgar and think they are so cool and think they are the best player in the game than they really are not or they do excessive noise/trolling ingame. Also, people who don't use their maps to view incoming enemy into their base (like CS:GO and World of Tanks).

QTEs, permadeath, unable to be able to save anywhere/anytime, escort missions (only when the escorted NPC is AI-controlled with suicide tendencies)...

not gameplay but, when every NPC on the game stares at me, and you are not even talking to them, just there, standing, and they are staring... with their cold, dead eyes... creepy.

now gameplay wise i hate the modern hype of making your character a complete useless moron, that can't even open a door. I hate the need of certain NPC to be able to open a door, i'm not talking about some sort of scort mission, where you have to take the uselless science guy from poin A, to point B, walking threw the middle of bullet hell square, wich is hard, but legit (exept when the NPC decides to use his/her head to catch bullets/blades/bombs and keeps killing itself, making the task imposible) i'm talking about a simple wood door, that can be opened by kicking it (and is even worse, when the NPC open said door with a kick); you know, CoD/modern shooter scripted events.

other thing that always bothered me was the need to cross the whole city to get a key to open a door... a simple wooden door, while i'm packing enough firepower to win a war. Or the classic impenetrable, all mighty, knee high wall...I DON'T EVEN NEED THE ABILITY TO JUMP TO PASS OVER THIS THING, I JUST NEED LEGS, AND MY CHARACTER HAVE THOSE FREAKING LEGS. i hate level limitations, if i can see it, then i should be able to reach it... or die trying.

Tutorials/hints that pause the game then explain everything with a video.

QTEs.

Cutscenes that don't even load the game in the background.

Accepted quest limit - when you can accept only certain number of quest and have to finish/abandon them to get new ones (like in The Secret World, I think it was 1 main, 3 delivery, 1 group and 1 or 2 extras?). I just like to accept every quest on my way and then finish them in order of what is the closest right now (could finish few quests on my way to "quest X" but because of the system you are left running circles and let's not forget about "I need better skills to finish this one but I have to abandon it and finish another one to get the skill points")

Also, unskippable platform/puzzle levels in "kill them all" games. The best option would be the choice of 2 difficulties - one for enemies and second for platform/puzzle so people can enjoy either without annoyance of the other (I enjoyed fighting in God of War but challenges made me ragequit)

Backtracking - If you're making me travel to the other side of the continent to do a quest, let me turn it in over there.
Invisible Walls - Even a plain, rock cliff is better than this.
Collect X Random Drops - If I have to halt my progress in order to pick up trophies, at least make them drop on every kill.

Time padding, as in when something that you could do in say 10 seconds is artificially made to take you 20.

For example : Say you are doing a quest in an mmo, your class is aoe based, quest makes you fight a single monster at a time instead of letting you round them up and aoe them all.

Other example : You are in an FPS game and instead of being able to say jump out of a window, you are forced to go up to it and press E.

Basically, artificially trying to make the game longer and therefore have a longer "time to beat" >_>

Timed missions or sections of the game. I like to take my sweet ass time, explore pretty thoroughly and backtrack if i want to. Hate being rushed and its especially aggravating if i fail a particularly long timed mission. Nothing will make me ragequit faster.

Moving slower than a senior, jumping like a fatty, running for a few seconds, useless flashlights.

I'm basically echoing other people, but...
1) Anything timed. That includes quests that fail if you don't do them within a set amount of time (in-game or real-world time), especially when there's no indication that it will be an automatic fail if you don't prioritize it.
2) Escort quests where you have to keep a character with really dumb AI alive.
3) Inability to hide/delete failed quests from your quest log, or hide/delete/sell items in your inventory that are now useless, or just clutter that you can't get rid of in general. Especially if you have limited inventory space and you pick up items that are now forever stuck in your inventory taking up valuable slots.
4) Inability to save whenever or wherever I want.

Guarding inanimate objects with health. Buildings, walls, doors, towers....Tower defense in general, when it's suddenly in a non-tower defense game.

Pointless boss fights, especially if they require you doing something repetitive.

Pay-to-win games

1. Bad combat system - mashing 1 key,quicktime events to finish off enemies(first 1-2 times is cool but then its just annoying), op combat elements(fable 3 magic....) 2. Bad designed bosses - too easy or too hard and not rewarding at all. 3. Too linear and/or boring(dont have charm) games(most annoying at all).