Rubber-band lag.
The Rubber Band Lag Dance.
Pop-up "how to fly a banshee" windows when I'm replaying a scene with a banshee to steal after finishing the whole game twice.
Frickin' one-shot insta-kill throwing knives that make my thirty rounds of .45 ACP utterly irrelevant even if I do fire the whole lot into his chest before he throws the knife because THAT's not enough to kill him.
Medics who get so much extra health they can survive being launched 200m down the road by an artillery shell going off under their heels.
Defeated enemies getting ten seconds of invulnerability when a medic revives them, so I can't finish them off but they can kill me.
Dickhead teammates running through my frigging mine-field while I'm laying it so it blows up in my face, ON PURPOSE.
Getting hit in the head by a single shot from a sniper who's 400m the far side of a concrete wall and can't possibly have seen me yet. If I'd been hit by chunks of wall after a tank shell hit it or someone had fired a 12.7mm MG into the wall and some of the rounds had hit me or the sniper had seen me move up to that wall and then shot where he thought I'd be lurking and got it right, I could handle that, but him being able to see and shoot through walls at that distance is just STUPID.
Having to sit and listen to the "assistant" guy say "Yyyyoooouuuuu ... jjjuuuusssstt ... fffoooouuuuunnnnndd ... aaaaaaaaaaaa ... nnnnneeeeeewwwww ... wwwwaaaaayyyyy ... tttoooooooo ... ssssssuuuuuucccckkk" after each song, even if I got 99.5% on it. (Fix: edit the sound files and replace all of his with 0.1s of silence.)
Not being able to turn off the feature that's dropping my frame rate to 2 fps.
The strange way clicking on something seems to get harder when I'm in trouble. Nothing going on, I can click the target then click the power and it works fine, but as soon as I really need to do something fast clicking the target doesn't seem to work for no good reason and every click on the power just drags it a millimetre and lets it snap back into place rather than activating it. It wouldn't be that hard to come up with a minimum drag distance for non-combat that counts as a click and a longer minimum drag that counts as a click in combat. It really wouldn't.
Moronic NPCs who run onto a bench and then can't get back down off it during an escort mission or get stuck between a lamp-post and a post-box while trying to reach me to give me a reward and then don't even acknowledge me when I'm right there in their faces trying to shove them back a bit.
Lies, like "You can get arrested for that." I've done that all over three flavours of Guard and none of them has done anything about it. Also powers that turn out not to do anything. I thought I was so clever, taking Levitate Other for that rescue mission, but the stupid NPC doesn't actually levitate up out of the pit, does he? Nooooo. The dancing girls make all kinds of offers, but can I accept them? No. Talking scenery, not NPCs!
Auto-target being retarded. I, Thog. Thog strong. Thog have mace. Thog smash. Thog go cave. Things. Thog smash. Things bite. Thog smash. Thog strong. Thog smash. Then the helpful young lady in the blue robe casts a heal spell on Thog, and auto-target targets her. It also doesn't much help when auto-target wants Thog to hit the Thing at the far side of the group. Thog arms normal long. Thog reach normal. Thog smash here. Things crunchy. Thog move. Thog smash there. Really, Thog can understand this concept just fine. There's room for subtlety in auto-targetting, like going for the highest-level or the nearest-to-dead or the kind the players tends to click when manually targetting or the one with the highest threat-level to health-remaining ratio, but the default basic assumption should be that Thog wants to hit the one nearest to right under Thog's mace.
The unique (afaik) Asheron's Call melee bug: if auto-target targets something and you start to attack it and then it runs away and you break off that attack, target the nearest enemy and attack that instead ... you get stuck for a full minute (I timed it) able to run around but unable to attack anything, switch weapons, use a shield, pop an ejector seat gem, use a healing kit, drop out of combat mode, drink a health potion, cast any spells or do anything but run around. Then when the minute's up, you try to attack the first one again. THEN you can take control of your character again. The fix is to make sure the power bar has blanked out after you break off one attack before you start another, but if you forget that you can get into trouble fast.
The place where the kid / guy who's been playing this twelve hours a day for a month can hop, skip and jump from barrel to porch to telephone line to plastic gutter to television aerial and into the air and launch a grenade that bounces off the tree, through the broken window, down the stairs, off the umbrella stand and onto your spawn spot then explodes 0.1s after you respawned.
The moment during the loading screen pause when the background sound effects and master volume suddenly go to 100% volume for two seconds.
Another game-specific one, for Daggerfall. Yes, I know it's old. Daggerfall was a single-player multi-sandbox game. There were half a dozen sandboxes, a couple of rockeries, several grassed play areas, the hopscotch board and the climbing frame and the car park and you could play anywhere in any of them. Cue grid-searches for the dungeon entrance. The main story was a sequence of quests, mission, murders, muggings and yawns that were set to happen after you'd achieved particular things. On your way to achieving those things, you could do all kinds of side-quests ... mostly consisting of "go here and kill these," "go here and bring this" or "Hang around and kill a few thieves or assassins or some such." All of these affected people's opinions of you, which is all well and good, but the game didn't just save the opinion scores. Nooooooo. It saved all the details, so when you were wandering around looking for work and asked about "latest rumours" you could be told that Grisiwald Gandahar's daughter was saved by a brave High Elf. Being the only High Elf in the entire western half of the continent makes this seem unlikely to be news, as such, but hey, it's nice that they've heard of you. The problem? To start a new game takes ten seconds. To load a new game save file takes one second. To load a level two save file takes twenty seconds. To load a level twelve save file takes fifteen minutes. Seriously. Save somewhere safe, because when you finish reloading that file you're going to be downstairs doing the washing up after the meal you prepared and ate while it was loading, or cleaning up after entertaining yourself some other way.
Another Daggerfall problem that also applies to some other games: I am the single most powerful person in this country. I can slay liches. I've done that. I've collected enough harpy tailfeathers to cover that wall. I've defeated a dozen assassisn sent after me and two dozen sent after other people. I'm using a sword I took for a vampire lord who died looking surprised and scared. I can spit acid fifty feet. I can chew six-foot tunnels through granite. My money bag is made from the cloak of a Black Reaver. My shield is part of the carapace of a giant queen bug that had terrorised three whole city-states for twenty-three years before I found out about her. I've personally set assault ships on fire off the Tannhauser Gate. Somehow I still can't shove the damn cat out of the way and open the door and can't just slot this traitor who's trying to sell us all to Hell. No, somehow I have to let the city guard mess up trying to arrest her again and then track her down and use this special tranquiliser dart gun to interrupt her magical abilities to she can be teleported back into jail and ... guys? Why don't I just summon a volcano and drop her in it? Seriously, I can do that.