In Medieval 2 Total War, half the Scottish units are wearing kilts and that just ruined the Scotland faction for me. Because nobody fucking wore kilts until the 16th century. And then, only the Highlanders wore them, if I remember correctly. And in the game, all the generals are wearing full plate mail armor and...nobody wore such fucking armor until the 1400s. Seeing some douchebag in full plate mail armor during a battle in the year 1150, for example, just ruins the mood for me.

And in Napoleon Total War, cannons are extremely underpowered. I've seen cannon balls hit enemy solders and then later see those soldiers get up, pick up their musket and get back in formation. WTF. Were my cannon balls really NERF balls or made of chocolate or what???

North Korea somehow having better technology than the south-Homefront

Russia only invading the USA when its in the most disadvantageous position-CoD

Being able to send tributes to allies while being walled up and not having any contact/trade route with them-Age of Empires 2

War elephants stepping on your own men and they still survive-Rome 2

Cutting people into a million pieces and them still get up and attack you-Metal Gear Rising

Cardboard Box-MGS

This annoys me too. So unrealistic. Russia would never invade the USA without first conquering Western Europe.

I'll also throw my hat into the "magic magazine" trope. I see people playing shooters where they are loading a new mag, literally, after every kill and all I can think about is this character carrying around a bunch of almost full magazines.

Even though Doom is a genuine classic and one of my all time favorite shooters, the Chaingun always bugged me. Partially because it was actually a Gatling Gun, and partially because it uses the same round as the pistol. So either the standard issue Space Marine Pistol fires extremely overpowered rounds, or the Space Marine Chaingun is severely underpowered. Although now that I'm thinking about it, none of the enemies are armed with pistols, they all have some type of rifle that uses the same round as the pistol.

I was much happier with how they handled a similar weapon progression in Half-Life. Both the starting pistol and automatic weapon shared the same ammo, but were clearly a 9MM Glock and MP5 respectively. Then the HD pack came out and changed the MP5 into an M4 variant, which ruined the whole thing for me all over again.

I also had a hard time with STALKER in that the rifles were backwards, that is they were ejecting brass the wrong way. I had to install a realistic weapons mod after a few hours of playing because it was driving me nuts.

Goddamnit, that was funny :-D And that video illustrated my point perfectly, even though it's fake.

Humans can actually survive the vacuum of space for a very short time. The important thing is to exhale first, otherwise your lungs with be blown apart.
http://www.scientificamerican.com/article/survival-in-space-unprotected-possible/
http://www.todayifoundout.com/index.php/2012/06/you-can-survive-being-exposed-to-the-near-vacuum-of-space-for-about-90-seconds-with-no-longterm-damage/

Hey, be fair. After 3 or 4 "I'd like to fuck you" options there was one at the bottom that said "piss off, asshole."

which is something that 2001 both book and movie got right

exhale and keep blinking otherwise your eyes will freeze over

Also thigh-high walls and fences that you can only go around, not over. I'm looking at you, cover-based shooters.

This!

What's that? It's locked? Ok, pick lock. Right I'm not a rogue, I can't. Smash it. There's no option to smash it... Arghhh! How am I supposed to get what's in this chest then?!

OCD and unopenable chests do not go well together.

People that are knocked out cold, stay that way for the rest of the level, eg Thief :P

Neverwinter Nights too, if I remember correctly.

I remember some games (or NWN modules?) that allowed you to smash every loot chest instead of picking the lock, but with a certain risk of destroying its content in the process. So force was always a viable way to get to your loot, but sometimes it ended up being nothing but glass shards and other broken stuff. ;)

(Compare that to action RPGs where smashing barrels and chests is the only way to get your loot in the first place. You smash a barrel so hard that the potions contained within fly all over the place, but no drop of liquid is spilled.)

- Casually looking through/vandalizing people's belongings without them seeming to care one bit - most RPGs, though not all thankfully. Related to that: oblivious store owners that don't seem to mind if you and you're entire party decide to see the shop from his/her vantage point behind the counter. The innkeepers in Neverwinter nights were especially laid back with one NWN2 not caring one bit that I broke down all of the doors of his rentable rooms.

- Dune2 started a trend that continued for a very long time: tank cannons do very little damage to infantry. Even as a kid I went: "huh?" At least the tanks can run the infantry over :D