The late-90's budget game Extreme Paintbrawl was the absolute king of this trope! The game's developers openly admitted that the game was shipped without any AI routines for your squad mates. So, at the beginning of a match in an enclosed arena, they would simply run into a wall and get stuck in it. Meanwhile, if you were playing in an open field, they would either flail about like they were having epileptic seizures, or bend down and crawl back and forth.
AI in Shadow Ops: Red Mercury weren't the brightest bulbs in the shed. Enemy AI would run right out into the open, even past the player's AI teammates, just to shoot at the player. Teammates fared no better as they would ignore said enemies completely.
Your squad in Brothers in Arms tends to stand in the open a few feet from cover unless prompted to move, apparently prefering to let jerry ventilate them.
In Deus Ex, and a number of similar games, the AI is usually pretty good...but will ignore the dead or unconscious body of an ally unless he was killed within sight of it.
One of the designers of Deus Ex said the AI had to be reined in a bit because players were rounding corners and getting shot in the head by entrenched guards, which obviously put a damper on the fun.
Another fun fact: enemies on patrol always turn left. Which, in essence, means you're up against the cloned army of a Mirror Universe's Derek Zoolander.
People in this game do not take well to friendly fire. Normally, this is bad for you, because if you shoot a friend a few times they will turn on you and kill you. However, if you dodge between enemies, they will sometimes get overzealous and shoot each other. This can be hilariously exploited to drive everyone in UNATCO insane (2/3rds of the way down the page), or it can be used to get Nicolette to single-handedly kill a pair of MJ12 commandos.
The most viable way to avoid the enemies in System Shock 2 wasn't sneaking but ... jumping on the nearest table or otherwise elevated position, because the AI only checked the floor for targets. While this can be handwaved with performance reasons considering all the objects on the tables this can be quite immersion breaking in a Survival Horror game with Breakable Weapons and scarce ammo.
In Doom 3, any monsters without a projectile attack (i.e. zombies, Pinkies, or Wraiths) had absolutely no idea what to do if the player jumped on a table out of their reach. So they'd just run in circles around the table while moaning their hearts out.
The enemy soldiers in Crysis are completely unable to deal with your cloaking device, making it a Game Breaker. You can uncloak, shoot an enemy in the head, and recloak, and all the enemy's buddies will just stare blankly at the spot you were standing just a few seconds ago. The expansion pack Crysis Warhead fixes this by making the A.I. fire blindly and/or throw grenades at your last known position, although you can still pwn everything in the game by simply moving a few feet to the left after recloaking.
The artificial stupidity in Crysis does not end there. In some situations enemies will outright ignore you even if you stand right in front of them (like they were unable to change their plans in the mid of getting somewhere). Truck and boat pilots will outright ignore you even if you hop on their head. Enemies will sometimes kill themselves eg. by running to the middle of a minefield or drowning themselves. If two enemies are talking to each other, you can sometimes sneakily kill one from the distance, and the other will be blissfully ignorant about anything and keep going on like nothing had happened.
In Half-Life, if you have a security guard following you during the segment with the trains, they will have absolutely no second thoughts about stepping onto an electrified rail line and instantly killing themselves if it is the only route to get to you on the opposite side of the tracks. And sometimes even if it's not.
Revolutionary at the time was the ability of enemy soldiers to make informed use of cover and grenades, running around corners to escape explosions and throwing grenades into the player's cover. One other thing they could do was set grenades as traps while retreating; however, more often than not they would be distracted by the approaching player's gunfire while setting the trap and return in kind - immediately forgetting that they were standing above a live grenade...
The friendly HECU marines in Opposing Force will sometimes either stop following or turn on you for no reason.
In Half-Life 2, many of your allies don't seem to understand the concepts of "I'm blocking Freeman's way" or "maybe I shouldn't stand in the narrow hallway".
The enemies with guns frequently run out, aim at you, and stand still while shooting, frequently in the open in a hallway or a similar location.
There's a similar glitch in the Sentry AI in Team Fortress 2. If there is an overhead obstruction and you can see the sentry's tripod, it won't see you unless you crouch to see the rest of it.
Your squadmates don't seem to understand that stealth and evasion are sometimes important. They will run headlong into sniper fire every time without a moment's hesitation, and upon encountering a strider, the black guy you join up with toward the end of "Follow Freeman" started shooting at it with his submachine gun, drawing its attention to both him and the equally ill-armed player.
Oh, and in Episode One you have to escort several waves of them safely past increasingly thick Combine fire. If they were just smart enough to run full tilt along the predetermined path, they'd probably all make it, but it wouldn't be a proper Escort Mission without suicidal NPCs, would it...
It is possible, through unusual circumstances, for an entire group of resistance fighters to kill themselves if you leave them in a bathroom alone, since they can trip over the bathtub and break their necks.
The AI survivors in Left 4 Dead can be like this. They usually wait a few seconds before actually deciding to catch up with the player and if you get attacked by any special infected other than a Tank, they may prioritize shooting regular zombies instead of trying to free you.
Made worse in Survival and VS mode, where the modes have a melee attack cooldown effect and the computer keeps trying to melee zombies off them when they have to recharge. Most likely a programming oversight by Valve and has yet to be fixed.
AI survivors also will sometimes fail to realize when you're lying on the ground right next to them, incapacitated, and just stand around and let you die if you are on ground that is slightly higher or lower than they are.
Sometimes the special infected may not be stuck, but will try to attack you from a position where you will never get hit and will keep doing it if you don't move.
On a more optimistic note: you can make the AI survivors act slightly less stupid if you use the macros to order them to advance. This doesn't fix anything else, but at least they aren't a room behind you all the time.
Left 4 Dead 2 seems to be much worse with survivor AI now compared to the first game. The AI will now usually leave you to die if you are strangled by a Smoker 2 feet away from them if there are common infected near them and even if you are perfectly several feet away from the AI in a straight line and are being pounded by a Charger, don't expect the AI to start shooting until they are at least in half the the range from them to you.
Also the same problem with Jockeys, but made worse since Jockeys can move you and Survivor AI seems to be incapable of doing more than one action at a time when they move. If you get ridden by a Jockey, Survivor bots will opt to shove the Jockey off when they are not close enough to do so instead of, you know, shooting it.
Survivor AI also get easily confused when multiple players are incapacitated. The bots either go back and forth trying to decide who to revive or may ditch you to try and save someone else that is close to death, even if they are too far away to be saved in time. When it's another AI player in trouble, though, they instantly drop everything and save them in no time at all.
Survivor AI are bad in dealing with special infected in VS mode. It is possible for the AI to keep shoving you and then run off, never bothering to shoot you, or are too slow to notice that you are slashing at their backs.
There's a theory that nerfing the survivor A.I. was a way of increasing difficulty. The general consensus is that they went a little bit too far...
AI survivors will blindly stare at a witch and slowly walk around her even though she is being aggroed. This can be extremely annoying in Hard Rain, where the entire level is filled with witches.
They also will never LEARN the concept of "Fire = Hot" and will gladly attempt to run through a fire to get to you. Problem is, they do know to run back when damaged by a level hazard (such as, say, fire) so they will just run back and forth into the fire until either the fire dies or they get incapped if there's no other way around, instead of just waiting for the fire to disappear. They are also oblivious to a Spitter's acid pool and will stay in the puddle until they start taking damage instead of running out of it as soon as the acid begins to form on the ground or other surface.
The Bots are actually quite intelligent when you're nearby, being practically aimbots. However, once you are a good distance away, they will forgo all other common sense and try to keep up with you, including but not limited to: Forgetting to shoot, forgetting to use a bridge, forgetting they're being chased by a tank, and forgetting pounced/snagged comrades.
On the other hand, AI infected are actually extremely intelligent. They will actively hide from your view until they've prepared to attack, Spitters will run and attempt to die in choke points, and will use a combination attack (such as a Charger plowing through people before a boomer comes and slimes everyone, or a Hunter will pounce and a spitter will spit on him to deal extra damage and deny others from simply punting the hunter off) against the Survivors.
The Special Infected do have a few quirks, though. For instance, while they often do hide, their hiding places don't always cover them all the way. You'll sometimes find a Hunter or Boomer trying to hide behind a lamp post. Another thing is, Hunters and Jockeys will pounce on survivors in the middle of a non-overwhelmed group, resulting in attacks that can be measured in hundredths of seconds before they're killed. Also, the Jockeys have no concept of ambush, running straight into quadruple gunfire if it means getting closer to a human.
AI survivors also love to shoot through human teammates and throw off their aim, especially if said humans are trying to make precision shots with the hunting rifle or sniper rifle. The only positive here is that AI survivors are incapable of harming teammates regardless of difficulty.
Bots will also shoot any Infected on their sight. Even if said infected is in front of hazards like a Crescendo Event that is triggered by shooting something or in worst cases, when an Infected is near a Witch. Fortunately they can't anger Wandering Witches when they shoot them, but good luck with normal Witches.
On the other end of the spectrum, the Common Infected love climbing stuff. Even if it makes no sense whatsoever. If something is in front of them and the Survivors are near it, they'll probably try to climb it.
Special Infected Bots also have no concept of fall damage. It's not uncommon to hear AI Boomers or Smokers leap to their deaths and explode behind you. It's even more hilarious when you see it for yourself.
Taking advantage of the Common Infected's lack of height perception, i.e. chucking a vial of Boomer vomit out of a hotel window, is not only a hilarious way to quickly clear a building, but a satisfying one too, as one cannot help but snicker as hordes of zombies run straight past the Survivors and willingly throw themselves off a building.
Team Fortress 2 brought out AI bots after launch in an update patch. Originally some bot variants proved quite difficult, such as Heavies and Snipers, whose pinpoint accuracy and wicked reflexes made them a Game Breaker in their own right. However, those issues were smoothed out to an extent, but there are still some fairly dumb AI moments.
When the bots debuted, the pathing in Attack/Defend and Payload maps was awful: BLU bots would all crowd on/near the Payload, making them easy pickings, and the RED bots would repeatedly ram themselves against the back wall of the Spawn, thinking that to be the shortest path to where the action is. This has since been more or less fixed.
Engineer bots are prone to some serious problems concerning placement issues for their gear and their own survival. This is most obvious when, for instance, an Engineer sets up his sentry overlooking an important area with its main arc facing a wall or pylon, obscuring a good 90 degrees of its targeting arc. Furthermore, some engineers will alternate between forgetting to wrench their machines to repair them, and forgetting to do anything but whack their sentry with the wrench. This ties back to their placement problem issue, in that they will often sandwich themselves between their sentry and their dispenser, leaving their sides wide open to enemies. This leads to scenarios where even the laziest sniper can simply peer across the map at them, line up the Laser Sight, and hollow out that apparently already-empty hard hat. They also have an apparent blindness to spies, continuing to bash a sapped machine even after the sapper is removed, leaving their spines open for surgery.
Medic bots have a tendency to forget to turn their healing beam on their allies or forget to watch their backs, again, opening them up to knives, flames, and scatterguns. They will also pop an uber the moment their heal target takes any amount of damage, even if it's from a puny pistol shot and that Heavy has yet to lumber across the map to his destination. Finally, they have an odd tendency to forget that they have a syringe gun, even if they've used it previously, and will run from even critically wounded enemies who would go down in one or two syringes if they attacked instead of retreated. Many a bot arena round has been lost because the lone Medic ran from a 3-HP Scout... and committed suicide when back in the spawn room.
Pyro bots wisely know to use the shotgun instead of merely acting like Leeroy Jenkins and charging with the flamethrower...but this is nullified somewhat by their apparent love of the airblast, where they will waste nearly a third of their ammo just bouncing a Heavy back before charging in to burn them—a Heavy that is still shredding them with more boolet.
Scout bots will rely excessively on their pistols, sometimes hanging off at the edges of the battlefield and contributing small 8-point chips of damage, instead of going in close to use their extremely powerful Sawed-Off Shotgun. This leads to instances where Scouts hanging out near their own rear lines are easily picked off by Snipers and Spies, two of the classes they counter best amongst human players.
Heavy bots have an ammo management problem, in that they seem to forget how much they actually have. They will often stand on a point and hold down the trigger for two withering seconds and promptly run dry, leaving them to try and keep fighting with their much slower, less devastating shotgun, or scurry off for an ammo refill, no doubt feeling quite embarrassed. Some will keep firing for some seconds even though they're out of ammo, which seems to happen most often when ubered.
Soldier bots, like Scout bots, will rely too much on their secondary weapon. Having exhausted all their rockets in their current clip, they will switch to the shotgun and empty it as well, then fumble reloads into the shotgun instead of the much more powerful rocket launcher which reloads faster than the shotgun.
Demoman bots, alternatively, forget about their secondary weapon, the sticky bomb launcher, and fight primarily with the grenade launcher. While this is not necessarily bad, the sticky bomb launcher is incredibly versatile and the bots will drop them to retreat—a perfectly serviceable use, until you watch the bot forget about them entirely and come charging back at you. Through its own carpet of stickies. Stand just close enough, and Demoman bots will detonate their bombs as they approach, blowing themselves to kingdom come.
Sniper bots are smart enough to know when to switch to their secondary weapon, and when to listen for sounds around them. However, they also seem to only think about line of sight, as opposed to cover, and quite a few Snipers will stand in fairly obvious places to take their shots. They will also try to take shots while sitting in the safety of the spawn room, when there is no way for their shot to hit anything but a wall or door. Sniper bots, if left alone, will sometimes sit in the spawn room the entire match, scoped in, staring at the door.
In Mann vs. Machine, robot Snipers rely exclusively on fully charged body shots to kill as to give the human players a chance to find and kill them before they get a Total Party Kill.
Finally, Spy bots are... not entirely implemented, and rightly so, as they are the class with a difficulty curve so steep it counts as a cliff but also extremely dangerous. They know how to sap, how to disguise, how to backstab, and how to use their revolver. In theory they should be able to operate loosely as their class profile dictates (the inability to cloak is of course an issue). In practice, Spies will sit in the spawn room as often as Snipers, if not more, wearing a mask but not actually moving. They also prone to spoiling their Paper-Thin Disguise, but that is simply because being convincing is difficult when they cannot attack. They also have very odd backstab usage rules, in that they will sometimes skip an obvious stab in favor of shooting, and sometimes forget that they have a knife at all.
These are lampshaded in the Team Service AnnouncementFake Players. All the bots can be told apart by their frequent idiocy, such as running into walls, not seeking health when weak, and using the wrong weapons for the wrong situation. The vid intends to educate about "bot servers" that fake having people in the server, thus attracting more actual players, by having bots play using fake Steam accounts (rather than the server-based bots they're supposed to use, which stopped counting toward the player count displayed on the server list shortly after bots became available).
Some particularly stupid bots won't even make the distinction of the weapon they are using. This can lead to some ensuing hilarity when an engineer starts shooting his sentry with his shotgun instead of using his wrench to upgrade/repair it. Though it can also be particularly annoying when a medic will follow you, relentlessly blasting you with needles, thinking it's a medigun beam.
The Dark Sims in Perfect Dark know exactly where you are and will usually hit you when you're moving. The Meat Sims are lucky if they hit you when you're standing still. Unfortunately, "always hit" and "shoot to miss" mean "with bullets that hit almost instantly": rockets are slower. This means you'll run away from the Dark Sims' shots and into the Meat Sims'.
If you play a custom game against Meat Sims with at least one of the six weapon choices being explosive, then that team will have a negative score from all the suicides and team kills.
And let's not forget Elvis in the Single Player Campaign. While he can be helpful at times and can always pinpoint cloaked enemies, if he gets himself killed then you have to start the entire level all over again. Can be especially bad on Attack Ship, where he simply stands out in the open and fires while the enemies fire back and charge at him. It can be a struggle to keep him alive for the entire level, sometimes you'll have to charge in ahead of him and take the enemies out before he gets too close. Luckily he isn't in too many missions.
Far Cry Vengeance has some pretty bad enemy AI. You can run up behind them making lots of noise and they won't hear you. You can stand right in front of them and let them shoot you and their accuracy is so bad that it takes a long time for them to inflict enough damage to kill you. You can even THROW GRENADES AT THEIR BACK and they won't turn around.
It can be bad in the original game as well. If you somehow manage to lure a merc into the water he'll just stand there, trying to fire his jammed gun (even if he's only knee-deep). You can pretty much keep throwing rocks at him until you get bored, and then leave him behind.
Far Cry 2's AI has some interesting ideas about turrets and vehicles. When two AIs are in a boat or truck with a mounted gun, and you kill the gunner, the remaining AI will stay at the wheel and keep coming straight towards you (as if the gunner were still there) while ignoring cover, even though it is completely defenseless while doing so. In the rare case that it survives long enough to actually reach you, it often just sits there at the wheel and looks you straight in the eye, waiting to be killed. In general, the AI is a good case study showing why combat drones IRL still have human pilots.
Another thing the AI does is to run into fires and burn to death, even those it started itself.
It also tends to stand behind partial cover, then start shooting at you when it has a minuscule chance of hitting you. By the time it has completely emerged from cover, it will need to reload. While it reloads, it does not move.
The AI controlling the wild animals you sometimes see isn't too bright either. If you park a car in just the right way, a fleeing gazelle will charge headlong into it and collapse, dead, upon making good friends with the stationary bumper.
Another rather badly implemented AI quirk is that the competence of your allies and the enemies are equal, so on easy mode, you would have to work quite hard to save your buddies as they can't hit a barn, but on hard mode, your buddy will generally manage to massacre the entire ambush before you get to him.
The animals in Far Cry 3 aren't particularly bright either. When non-predatory animals (like deer) get startled, they will run away in a random direction as fast as possible, including directly into nearby bodies of water. As soon as the water gets at least knee height on an animal, it will then drown instantly.
The Halo series has marines that are downright stupid at times. In the first game they had no concept of stealth, making otherwise very easy rooms of sleeping grunts annoying when they ran with guns a-blazing, waking up the aliens. In Halo 2 and Halo 3 they learn how to drive. AI drivers will run you smack into walls (leaving you completely vulnerable to tank fire), or careen straight off cliffs, or ensure completely avoidable rollovers happen... and AI gunners aren't much better, as they seem to be attempting to conserve ammo on a turret with Bottomless Magazines. So on single-player campaign mode, you have to drive for yourself, get out of the car, then gun for yourself unless you want to stick around a single map for half an ho. This is exactly why the entire series has co-op.
The dropships also seem to like dropping warthogs on players sometimes. Most infuriating.
Despite the overall difficulty of Halo being quite high, the AI tends to be pretty stupid, relying more on numbers, superior weaponry, infinite ammo, vehicles, high damage resilience, improbably high accuracy, and level design in their favor to serve as a threat. Many enemies will not react at all to getting shot if you are not within a specific range or attack them from an area the developers probably didn't consider when programming the game. Most enemies don't react when their allies die near them (Grunts tend to be the exception, but their response is to run around in panic). On the other hand, they are often devastating once you walk into the programmed scenario they are waiting for.
Conversely, the enemies exhibit Artificial Brilliance on Legendary difficulty, especially in the third game.
It hasn't gotten any better in Halo: Reach. Allies will still blow themselves up if given the rocket launcher, stand still right under enemy dropships, and charge straight at Hunters. The ODST "Bullfrogs" in the mission "Exodus" will even jump right off cliffs to their death. Certain enemies, like Elites, will sometimes stand still even as you're shooting them.
Why single out the non-spartans in Reach? We're meant to assume that these soldiers, brought up from childhood in a military acadamy, can't drive any vehicle for cookies and their entire battlefield strategy is to walk left and right while shooting unlimited ammo at an enemy. If they weren't invincible they would be dead in seconds.
Kat in particular gets a special chance to demonstrate her idiocy in the third level of Reach's campaign. In a Warthog's driver's seat, she drives right into knife range of enemies wielding antivehicular weaponry and spends several minutes repeatedly making finicky three-point turns around plate-sized rocks; in the turret, she prioritizes shooting a Grunt who's half a mile away and behind cover over an Elite whose shields you just dropped and is currently meleeing the vehicle. On foot, Kat fares no better; she'll refuse to follow you to the next objective, charge in and alert enemies who you would otherwise have taken by surprise, and ignore her own advice by entering into brutal hand-to-hand duels with Hunters.
Friendly Army AI, though slightly more useful due to the ability to give allied troopers weapons, is still impressively hell-bent on dying at the hands of its own stupidity. Troopers are unable to differentiate between area-of-effect and precision weapons; therefore, they'll fire round after round from a rocket launcher at groups of infantry that include you, unload that Concussion Rifle into an enemy who's two inches from their face and kill themselves in the process, and charge into combat with enemies whom are currently being blasted to pieces by your tank. Their default response when stuck with plasma grenades is to scream and hurl their suddenly-explosive bodies at your feet. Reach introduced a "fireteam" mechanic where troopers who you meet up with are labeled on the map and get names, but more often than not it doesn't matter since they'll all be dead within seconds anyway.
In Halo 4 it seems that marine and Spartan AI became even more stupid since Reach, shooting at dead enemies was perfectly fine in previous games when they were shooting them after the fight is over, but now they're shooting at dead Covenant and Prometheans in the middle of a firefight and there are still half a dozen left firing at them. In vehicles they're even worse, their line of sight being smaller than Covenant AI in their vehicles, allowing them to shoot at you without any response from allied AI until you drive closer, and they drive pitifully slow whenever behind the wheel, leaving you exposed should you be in the gunner seat.
In the first TimeSplitters game, AI had a nasty habit of running in circles till you shot it. Annoying when the enemy does it, downright infuriating when your team mates do it.
Again, in TimeSplitters, on custom maps featuring inaccessible weapon spawns, the AI characters would just run around in a vain attempt to access the secret cache. On custom maps featuring NO weapon spawns, the AI characters would not move AT ALL.
In TimeSplitters 2, there was a map that consisted of two bases with a gorge in between, joined only by bridges. In some game modes, bots (both friendly and unfriendly) would start running across a bridge, then pull a 90 degree turn and run off the edge for no discernible reason.
The TimeSplitters 2 AI could easily be driven to laughable behaviour by the map editor. Make a map with two rooms, no starting weapons, and one gun in the second room and the AI players will march in a perfect conga line over to the gun. When one gets it, all other AIs will stand frozen while the one with the gun shoots them. This in spite of the fact that there is a melee attack in the game; in fact, the player can punch any of the unarmed AIs to death and they will remain stock-still throughout the process.
Wolfenstein has all the classic artificial stupidity bugs. Most notably, the enemy players will not react to you at all unless you are within a certain distance of them (at which point they will know where you are with unfailing accuracy) meaning that, once you've got the sniper scope, you can snipe groups from a distance and watch as the Germans show absolutely no reaction to their comrades' heads exploding.
It bears mentioning that the entry for Artificial Stupidity on the Star Wars Battlefront page had all its examples removed and replaced with simply "a lot", because it was probably one-sixth of the page itself.
You will sometimes see such things as allied soldiers running directly into a wall repeatedly, or shooting at one for no apparent reason. The reason behind this is that the AI is programmed to move or shoot directly at enemy AIs, and seems to forget to account for intervening terrain. It gets worse on tiered battlefields, where your soldiers will cluster in an empty hallway because there's an enemy in the level directly beneath them.
Also notable is the AI's tendency to spam grenades constantly, even if there are teammates around. Sometimes indoor hallways become completely impassible as both sides' AI units just stand there filling them with grenades, re-spawning, and doing it again.
An interesting experiment is to activate invulnerability and see how many enemies die by clustering around you and getting blown up by allied grenades.
A second enjoyable tactic is to get in one of the Nigh Invulnerable tanks, wait for enemies to cover it with sticky grenades, and then charge them, mowing down entire squads of foes with their own misplaced explosives.
The "hunt" game type on Naboo has the Gungan team armed only with grenades. It's absolutely possible – perhaps even recommended, so as to avoid the massive grenade slaughter-fest that inevitably occurs – to sit back and let the enemy bots kill each other off because they simply cannot throw grenades with any reliable degree of accuracy.
The main way of increasing difficulty levels in the first game is to deduct 50 points from your allies' IQs. Defending objectives? That's for squares! Win or lose, a higher-difficulty game will typically end with the player having scored upwards of 80% of the kills or capture points on his team — occasionally, the player is the only one on the team with a positive score and would have been wholly better off playing alone.
The addition of space combat in the sequel also adds new chances for stupidity.
If you are flying, say, a Republic Gunship and give the "everybody out" command before you land, your allies will cheerfully jump out of the gunship, ignoring fine details like not possessing a parachute or jetpack, and the height being enough to break their necks. You then have kills deducted for every stupid clone you have thus weeded out.
If you land a gunship in an enemy hangar with passengers on board, all except one will get out. If you disembark without taking off and landing again, the one remaining passenger will grab the pilot seat and promptly crash into the hangar wall.
Same with two-seater ships like TIE Bombers, but there's another example involving those. If you get out of a TIE Bomber your co-pilot might follow you, get back into the bomber and then take off and forget that the ship is capable of both braking and performing turns.
A hilarious tactic in space battles goes like this: infiltrate the enemy's hangar, then proceed to use your free time to get in the enemy fighters. Don't leave the hangar, though; just get in long enough to turn the ship around, then immediately exit the fighter. The next time some AI schmuck comes along, he'll enter the ship and bravely fly forward...directly into the hangar walls. If you wanted to earn the points for that kill, keep your eye on the enemy's lightweight fighter (the A-Wing, in the Rebels' case), and simply plug a rocket into its backside every time someone goes to enter the fighter.
One of the most hilariously stupid AI actions in the game comes with the ability to perform evasive maneuvers in any flying vehicle. All too frequently, you'll see a scout fighter make a flawless bombing run against a capital starship while miraculously dodging huge amounts of flak, pull up and begin to fly away... then for no discernable reason, do a barrel roll and turn 180 degrees, sending themselves full throttle into the enemy ship. This is actually possible to exploit by firing a missile at a fighter flying directly away from its parent ship; the fighter will loop backwards to break the lock and power straight into the huge star cruiser right behind it.
Another enjoyable space-related action is placing time bombs on ships just before they take off. Rather than taking the sensible course of action by getting out and running the hell away, the pilots will happily zoom off into outer space, dying in a flaming ball of ship debris shortly after they leave the hanger.
The AI cannot use any transport ship at all in any capacity. Ideally they should fly in and land troops into the enemy ship. They can't do that. A decent tactic would be to use them as some sort of heavily armed fighter. Again, they can't do that. What they can do is fly around like an idiot and be unable to fire back as you get an easy kill from the incredibly slow transport.
All enemy units are basically forced by the AI into a single, identical game-plan. The implications of this vary; sometimes it just means that the AI ignores things such as the Engineer's ability to supply health and ammo to himself and his comrades, but usually it means Han Solo is prone to taking a seat behind a turret at Mos Eisley, shouting "Never Tell Me the Odds" as you casually shoot him in the back.
For the record, that single, identical game-plan the AI is forced into is always "grab the turrets and forget everything else". Given a choice between staying at a control point to deny the enemy the ability to capture it or staying in a turret, they'll pick the turret. Make the choice between going out and (re)capturing control points or staying in their turret, they'll pick the turret.
If you are a Jedi or any class with rockets, you will end up betraying teammates because when you try to kill the enemy, the AI on your team will stand right beside them.
Similarly, if you are a clone commander, stay far away from allies. They are only too happy to wander in front of your chaingun and die.
It bears mentioning that bots will virtually never try to lock on with a rocket launcher, instead firing blindly and sending rockets flying off across the map (or into their own troops). Tanks are virtually impermeable to all rocket-launcher-based attacks because of this, though they seem to have a little more accuracy shooting down snowspeeders. The one thing that they will attempt to lock onto are the Base On Legs AT-TE and AT-AT command vehicles.
Most of the bots seem to choose the human player as the primary target, regardless of whether you pose a direct threat, or if they are even within attacking distance. While sniping, it isn't uncommon to see an enemy stop dead in the middle of a firefight, draw their sidearm and begin taking potshots at your position. Even shooting an AT-AT walker with a pistol will sometimes cause it to stop in its tracks, and slowly turn towards you (sometimes a complete 180) just to return fire.
Judging by their habit of jumping in front of firing units, AI units believe themselves to be Friendly Fireproof. They aren't.
Enemies don't understand range, accuracy, or covering fire, and will therefore react to you sniping them by standing out in the open and firing at you with a pistol, never advancing, flanking, or even trying to close the range to a manageable distance. "Native" enemies (such as the Wookiees on Kashyyyk) have unlimited reinforcements and their deaths don't detract from hostile reinforcement count. Proper abuse of this error can result in upwards of 250 points, 150 kills, and 50 headshots in one life.
Vehicles offer many new and fascinating ways for the AI to be stupid. Pilots on the Hoth level of the original Battlefront have been known to have their flights abruptly terminated by, say, the ceiling of Echo Base, which they drove into for no apparent reason. Other times, the AI will abandon a nearly intact vehicle next to a hostile spawn point; respond to the Sabotage power in Galactic Conquest by driving off in a crippled vehicle rather than sitting on the repair droid that is right there; ignore an unoccupied and intact enemy tank, when stealing it could provide a massive swing to your side; take several minutes to respond to your order to get in; sit there stupidly and get blasted into spare parts by an AT-AT; or use speeder bikes solely for transportation without realising that you can do a lot of damage with them by using their underslung blaster, which virtually never needs to recharge and deals a surprising amount of damage...or by running the enemy down, which does even more damage and takes no ammunition at all.
AI Dark Troopers and Jet Troopers seem to use their jetpacks solely to fire at people from the sky, without using them to close with a spawnpoint or to escape an attack.
Classes that carry Recon Droids like the Magnaguard and Imperial Officer often deploy them at the worst possible opportunities - usually when they're out in the open and under direct fire, thus their character is a sitting duck while they try to fly the droid around.
Even if they aren't immediately killed, the AI only uses the droid to shoot at enemies with its extremely weak blaster, and never makes use of the more effective 'self-destruct' ability.
If you play as the Ewoks on the Endor Hunt, the Stormtroopers struggle to hit you at close range. And by close range, I don't mean a couple yards. I don't mean feet. I mean so close you are literally touching them and they still can't hit you because they're programmed to shoot at a man sized target's chest but not to adjust if the target is half the normal size. They also can't hit you with their sniper rifle because the foliage seems to confuse them and make them simply stare at you, unable to do anything.
In the same vein as above, if you decide to play Mos Eisley Hunt, you'll be pitting Tusken Raiders against Jawas. The Jawas will win almost every single time, because the Raiders cannot comprehend that Jawas are half the size of a normal human, and will consistently shoot over the Jawa's heads. It is possible to win as a Tusken Raider, but you're going to be doing basically all the killing.
Painkiller's AI wasn't exactly what you'd call Mensa material to begin with, but the Obvious Beta expansion Painkiller Resurrection takes this trope Up to Eleven, where enemies who can't deal with the erratic level design get hung up constantly on corners, curbs and other random bits of scenery as they try to charge the player.
In Strife, when you converse with the rebel soldiers while they stand around as NPCs, they sometimes warn you not to stand too close to the enemy's "Crusader" robots, due to said unit's short-range but highly damaging flamethrower. When these same rebels see active duty on certain levels, however, their AI causes them to attempt to close to melee range on their enemies, including Crusaders, resulting in many of them going to their fiery death like lambs to a slaughter. This is despite the fact that the rebel soldiers have no special melee attack; their only attack is to fire an assault rifle which works reasonably well from a distance.
Metro 2033 has the worst grenade throwers in the history of ever.
Fascist soldiers have an excellent awareness of cover. They'll duck, hide, peek around before stepping out and will call to each other. Unfortunately this often happens on the wrong side of what they've chosen to hide 'behind'.
Every Tom Clancy first person shooter game, such as Ghost Recon and Rainbow Six has often required the player to pull his own weight in a firefight, since the squadmates were often incompetent.
In Rainbow Six 3: Raven Shield, a fireteam left in a corner under AI control will inevitably cover the wall instead of the wide open room around them.
Also in Rainbow Six 3, a terrorist in an entirely different room is liable to hear your footsteps through the wall (bad enough already) and then proceed to throw a grenade. At the wall. Right next to them.
The Vegas sub-series is much worse in this department. Despite the removal of long, waypoint-based commands for your team, you will more often than not find yourself forced to step Mike and Jung through every individual meter between them and the door you want them to breach if there is not a straight, flat line between them and it.
In Ghost Recon: Advanced Warfighter, support choppers will wander into enemy hot zones and get ventilated by AAA fire, your teammates will bum rush the enemy in attack mode, and NPC's wielding the rocket launcher tend to frag themselves on obstacles.
In the eXtreme Paintbrawl games, if you send your team ahead of you, you will likely find them running into a wall next to a door. Unless they get eliminated in the first few seconds, which is also common.
Your Red Shirt Army allies in the Medal of Honor series tend to suffer from this, eg running blindly into the enemy's line of fire, not taking cover, or allowing themselves to be melee'd to death. This frequently results in mission failure during escort missions.
Golden Eye 1997 has decent enemy AI. However, enemies will only shoot at you if you are on the same elevation as you or close to it, so if you are a bit too low to them or too far up, they will move closer to you in order to get a better shot, even though there is nothing blocking their firing sight. This also gets worse if you park yourself on a stairwell since the AI will not even bother to shoot at you, even if you are less than a foot away. Because of this exploit, it can lead to an Anti-Climax Boss against Xenia, where you can shoot parallel to the bridge as she crosses it and she won't attack until she gets across the bridge and you can kill her before that happens.
The way AI works in this game is this: If the CPU can walk in a straight line towards you, it can see and shoot you. The inverse is also true. This can work to your advantage or to the CPU's, depending on the situation. If you stand just behind a rail, you can shoot holes in him and he'll have to come around to get you, but if there's a big hill that you can't even see over, they can shoot right through it and hit you.
Another way in which they're stupid is if one comes after you, but doesn't see you after a few seconds, it will forget about you, stop chasing you and stand perfectly still indefinitely until you get his attention.
Yet another way, there are some CPUs that are programmed never to move unless they see you. This means if you stand somewhere he can't see you (like behind a rail), you can shoot him all you want and he'll be oblivious to your presence.
The F.E.A.R. series is generally very good when it comes to AI, however that do make some cracking blunders, such as killing themselves with their own grenades and blowing themselves up by targeting flammable barrels.
One very common mistake (and often the only reason you're able to take them down in higher difficulty levels) is using cover from irregular-shaped objects or structures of the wrong size, which often leads to an entire squad of Replicas either with their bodies half-exposed or hitting their own cover while trying to shoot from their positions. And they don't always move when injured, meaning you can kill a Replica by gunning it from afar with the RPL, and he will not move to protect himself properly. That's not to mention the fact that they don't take explosive props into account at all - a perfect strategy to deal with groups is to lure them into a place you've cleared and let a barrel/extinguisher/fuse box behind. When they come, shoot the prop. Instant squad kill.
One thing of note is that the AI makes dumber decisions as you lower difficulty. Low-difficulty enemies have less accuracy and damage, which means they'll take stupid decisions like rushing into the bullet-time marksman wielding a shotgun.
Desert Combat, a popular mod for Battlefield 1942, rolled two of the original game's classes (medic and engineer) into one class, without updating the AI. This could be problematic when playing with bots. If the player's tank was injured, a helpful support-class bot would run up and begin covering the tank with anti-tank mines. If the tank moved an inch (and sometimes if it didn't) it would go up like a Roman candle. It gets worse, though. When the player's tank is hurt, the AI almost always spawns as support. Thirty seconds after the player was first trapped by his tank's thin coating of anti-tank mines, twenty more support bots would run up to festoon the tank further. When the mines ran out, the bots would pull out shotguns. When the shells ran out, they would melee it. A crowd of twenty bots, rhythmically beating a tank covered in landmines. The only bright side was that when you eventually did move, you'd take all those idiots with you.
This was just one of a number of AI screw-ups in the game. The most prominent was when the AI - which was never programmed to fly a helicopter - tried to fly a helicopter. They would often fly straight up into the air as high as they could and then attempt to turn. Soon after, the helicopter would inevitably crash into the ground, often upside down. Any attempt at recovery looked like a drunk, epileptic three-year-old was at the stick and God help you if you were within 100 feet of it, because there was a good chance it would plow into you while dragging sideways along the ground.
The enemy AI in Clive Barker's Jericho is very, very stupid. They generally do nothing more than charge you, and while for some enemies this is actually a good way to take out the Squad, for most it results in them dying before they get anywhere near you. The allied AI is also quite dim, as they don't quite understand the concepts of "retreating" or "taking cover" and will often melee the exploding enemies or dash up to enemies with ranged attacks and get slaughtered. Luckily, their death does not mean a game over unless everyone, including you, dies.
In Soldier of Fortune II, you have to escort Dr. Ivanovich near the end of the second level. He tends to follow you into the line of fire like a sheep to the slaughter, resulting in Game Over for you.
Conkers Bad Fur Day had multiplayer AI that, although justifiably stupid on the lowest difficulty level ("Inbred"), can sometimes become this even on the highest level ("Einstein") due to the lack of friendly fire protection.
Sometimes they fail to check what's immediately in front of them before opening fire, such as firing at you because the enemy was directly behind you, as if they expected the bullets to fly through you into them.
Other times, they'll shoot any and every friggin' thing that moves, including you (common when armed with sniper rifles and grenade launchers).
When they're not shooting each other in the back, AIs, friend and foe alike, will stand around doing nothing besides, perhaps, jumping, often conveniently out of your line of sight just to give the illusion that they're off doing something important or trapping themselves in a corner until you shoot or kill them (this tends to be common the less AIs you have running around on the map).
Depending on the mini-game, the AIs will also be focused more on shooting (with actually aiming being an afterthought) than the goal they're supposed to accomplish, such as how the weasels in Heist will focus more on killing each other than the money bags, and the only time the money matters is by making whoever's holding it Public Enemy Number 1, or how War!Colors will have the troops more focused on sniping at each other than either side bothering to grab each other's flags. On the other hand, it works in your favor at times; your foes are no smarter than your own teammates, and can even commit stupicide trying to kill you. A common scenario involves you being in an area where you're invulnerable (or not entirely in range of an attack), leading to your foe, armed with a grenade launcher or bomb, to fire at you, only to obliterate themselves by being too close to their own blast. This will, at worst, knock you up on the air and stun you for a while.
Red Orchestra has AI combat engineers that set timed explosives in the middle of groups of friendlies. Given the game's realism, this tends to be messy
In Quake, ogres always fire their grenades horizontally — so if you stand on a ledge above them, they end up blowing themselves up.
Psychos in Borderlands will often pull out and arm a grenade when low on health, charging at players For Massive Damage. They will even do so if there's no way that they'll actually reach the players before the grenade goes off. In all fairness, they areinsane and violent.
Also in Borderlands2, during a mission with an escort (Such as the Slab King escort quest around level 20), if you are in Fight for your Life, the escort NPC is likely to continue killing mobs you might be aiming at, and even more likely to kill your kill and leaving you for dead.
The AI in the Dark Forces Saga is generally pretty good. Enemies will react intelligently, and while they're not so great at seeking cover, at least they know how to fire on the move. That's for enemies with ranged weapons at least. Then there's the enemy Sith Mooks with lightsabers in the later games, starting with Jedi Outcast. It's easy to lose count of how many times one of them, especially one of the orange suited bottom-tier mooks, does an 'evasive Force jump' to get away from you if you knock them down or use a Force power on them . . . only to go sailing into a Bottomless Pit.
The last part of the Vjun levels in Jedi Academy are notable for two specific cases of this. First is a cultist on a balcony you have to get up to in the throne room: he's supposed to wait for you up there and attack once you're there, but most of the time he hears you as you enter the room and promptly breaks his legs trying to get to you early. Second are the twin Reborn Masters assisting the boss of the level - since they lack lightsabers, they can easily be killed with guns simply because neither they nor said boss will typically move from their starting positions until you walk closer.
Teammate AI in PAYDAY: The Heist are not too intelligent or speedy. Bots will usually fail to notice that you are being electrocuted by a Taser, even if he is next to the two of you. They will also usually be oblivious to a Cloaker who just downed you and will try to revive you, only for them to be instantly downed by the same Cloaker. Bots will also try to revive someone regardless if another person is already on the job, so don't be surprised if multiple bots attempt to revive the same player, which doesn't speed up the process. Friendly AI never sprint, which means that unless you want to risk being downed while your team is too far away, you have to approach most levels slowly so the bots can keep up. This was also made worse in a patch which made bots keep a bigger distance away from you when moving.
If you give an order, sometimes it can be overruled and ignored if something "more important" comes up. Examples include getting an urgent message on the radio, issuing multiple orders in a row, spotting a suspect, etc. This sort of makes sense, but can be frustrating when you later notice that the action you made still hasn't been completed.
Your teammates usually scan the room thoroughly before giving off reports like that. But some AI wonks do occasionally appear in more tighter or crammed-in spaces. Sometimes your teammates even accidentally shoot you if your squad is caught in a fire fight with the criminals. Sometimes they run in front of your gun while you're trying to fire. Or switch place in front of the doors if one of them is lacking the type of grenade you ordered to be thrown into the room. Which is of course logical... unless there's a friggin' suspect right in front of the door, mere centimeters away, ready to shoot them while they're waltzing in front of the exposed doorway. Most of the AI issues of your squadmates and problems with giving more complex chains of commands were thankfully fixed by patches and the Expansion Pack.
Many first person shooters feature a quirk known as "monster infighting" wherein NPCs, if they accidentally fire on each other, will then proceed to battle it out while the player either slips away quietly or waits for the carnage to end and picks up the spoils. The original Doom is the standard-bearer for this.
Mega Man 8 Bit Death Match, the bots are not the best things around, due to the limited bot support in Zandronum. This leads to such incapabilities such as being unable to chase players up ladders, and running on the spot over cliff edges. Thankfully, the latter has mostly been rectified in v3a now, with bots trying to "look" for any opponents if stuck on a ledge, although unfortunately it doesn't work in certain spots.
The original version of Burst Man's stage had a large pit of buoyant, pink liquid in the middle. The one CPU that would inevitably be spawned here would be completely incapable of leaving it, being unable to figure out the bouncy bubbles used to propel yourself out. In fact, it was almost impossible to lose on this stage in single-player mode, mostly because the AI had a tendency of camping out at the landmarks on the corners of the map rather than move around it looking for opponents, so it was pretty rare for anyone besides the player to actually score any kills.
The CPU does seem to have some amount of common sense, such as realizing that they shouldn't jump into lava. However, they won't know what else to do about the lava and will simply stand at it, even if they can jump over it. This is easily seen in Junk Man's stage, where the CPU will want to get their hands on a weapon out on an island in the lava, but instead of jumping across to it, will simply stand there staring at it, even letting you shoot it before they do anything.
Dynamo Man's stage includes a particularly funny example where CPU players seem to really like riding the giant conveyor belt running through the center of the stage. Because they have a level of edge detection that prevents them from falling off the death pit at the end, you can easily find about five or six CPU players accumulated at the end of it to be slaughtered with certain weapons.
The AI also cannot figure out the instant death Force Beams in Quick Man's stage and have been known to simply walk right into them and die.
Enemies in Nosferatu The Wrath Of Malachi have been known to do things like continuously run into walls or get stuck on objects. They also seem mostly incapable of opening doors.