Similar thing in the old RTS Warzone 2100. You eventually get to research a Satellite control building or somesuch, and once you complete the building the fog of war is removed. Lose the building and you're back to regular sensors, which are still useful even with the satellite building active.

"Everyone gang up on the human player"

Yes, this is exactly what I wanted when I set the game settings to free-for-all. It makes sense if you're pursuing a win condition, like wonder victory in Age of Empires, but when that's not the case it's just downright stupid.

it's part of game mechanics, actually.
but it really freaks me out when enemy in Perimeter takes my core towers under his dome and captures them. with game having no active pause just couple of seconds of your attention somewhere else are needed to lose half of your energy network.

The only annoying thing i can think of is when that god damn gym master heals his Pokemon with a high HP while you worked hard to get it low.

FPS games... Head Shots. I really hate instant kills on me. Mainly because it's annoying.

it did work in a game i played i think it was Tiberian Sun there was a AI harvester or AoE villager that was behind my town center/construction yard even though i explored the whole map i could not see it even on the mini map since my color was larger area so it covered up the ai color.

But for me it was RTS AI where if you go long enough they kinda give up an at the start they will hammmer you but after so long they start only building 1-3 units to the point you don't really need to do anything

In FPS games, enemies simply side-stepping my shots so that the only ways to hit them is either to spray-butllet everywhere, or go close to them and then shoot. I just feel enemies being that good at avoiding shots makes a FPS game unfun.

In my book it isn't even a sign of the AI being (or at least appearing) smart, it is just that the computer AI is using it to its advantage that it is doing all the calculations. Sure. i could also make a shooter game where it is impossible to hit enemies, they'd simply move away from the bullet 0.000001 s before it hits them, Matrix style. Same with those perfect headshots that someone mentioned, it would be very easy to make enemy AI that hits you perfectly 100% of the time, you can't simply avoid their snipers shots if they have a clear view on you.

For a single-player FPS games, the enemies need to be a bit "retarded" and slow in order for the game to be fun. For multiplayer online FPS games, it comes from the fact that other players also are humans with their more or less slow reaction times, being distracted by what happens around them etc.

Two games where I remember this were Unreal (IIRC) and Wheel of Time, ie. I became annoyed by many of the enemies side-stepping (or somersaulting) shots.

I hate it when some enemies are more likely to attack a specific race and/or class. Having a dwarf cleric in MM7 is very, very painful... everybody hits the poor gal/lad.

Exactly.
This is just an example of developers giving the AI unfair abilities to appear smart. As you said, they are just unfair advantages that computers can use over humans. I'm looking more for stuff that's completely fair, but nevertheless you find annoying.

No you couldn't. Not with today's hardware. ;)

Yes the Skaarj, and sometimes the floating eye things in Unreal dodge weapon fire very well at medium to long range. But it's stuff like the ASMD 2dry fire, Stinger and 8-Ball that they dodge, something that a skilled player would be more than able to dodge as well at that range. So you either have to close range, or use instant fire weapons against them.
Unreal is one of the few FPS games where the enemy creatures almost come across as human, so I think they did the AI very well. The botmatch in particular I always felt was very close to a LAN deathmatch experience.

Ugh. You mentioned that perfectly bland shooter. Take a great idea like Jordan's Wheel of Time and make a character that does ZERO to fit into the mythos of the already built world with a storyline that completely ignores the current narrative and a weakness in the power shoehorned in to make managing ammunition a thing. The series was screaming for a party based RPG, and they gave us...... that.

Endless grenade spamming in FPS's or Fallout 4. So cheap..... and I use the trick myself against the enemy.

This can be used to your advantage.

For example, in one dungeon from World of Xeen's endgame, you encounter tons of a very strong enemy called a Dragon Mummy (which, IIRC, counts as a dragon but not as undead). That monster will attack your cleric, is *very* powerful, and is also extremely accurate. Since the enemy attacks only your cleric, all you need to do is give her all the obsidian gear you have that she can use, use fountains and magic to boost her AC even higher, and she won't be hit much at all. Then, you can just plow through, only reloading when an enemy manages to land a hit on her; your other characters don't need armor (which isn't usually worth it in World of Xeen anyway). (Note that the AC required to not get hit is really high; I am thinking that 200 might not be enough here.)

Also, in Isles of Terra, protective spells are only single target, so if enemies favor attacking a specific party member, you only need to protect that one character.

Anyway, regarding annoying things enemies do:

In SaGa Frontier, enemies will attack fallen party members, causing them to lose LP (which isn't that easy to restore, and a character to 0 LP can't be restored without going to the inn or using rare items).

In Romancing SaGa: Minstrel Song, when enemies combo a character, causing the character to lose multiple LP at once, even if the character would have only lost 1 LP had the attacks not comboed.

I hate, with a passion, enemy AI that runs away and makes me chase them when I'm kicking their ass. Like the Elites in Halo- when their shield goes down they run away and hide to allow it to recharge. Perfectly legit tactic, I do it myself. But AI should just stay there and let me kill them!

Here's another one, though quite different from what I have posted before.

Specifically, Battle for Wesnoth, and in particular the Survival Extreme mods (each player controls one unit, you have to fight off hordes of enemies that get stronger as time progresses, and there are shops where you can boost your stats).

The AI, when it gets its turn, will take time to decide which unit should attack me first. The annoying thing is that it takes time for the AI to make this decision (especially when it has 100+ units), and given the nature of survival extreme, I don't think it matters much. In fact, a simple AI that would just attack with the first unit able to attack would be enough when it comes to survival extreme; don't waste my time with fancy AI routines when they aren't necessary!

(This issue could come up in plain survival, but it isn't as much of an issue in regular gameplay, as you normally have multiple units to control and the AI doesn't get nearly as many units, making the AI behavior more interesting and less time consuming.)