In Metal Gear Solid 4, the "Scarabs"— the little three-limbed orb/camera sentries — are a massive headache. They swarm at you twenty at a time, and if they get too close they can either knock you down (typically when you're in the middle of reloading) or latch on to you, therefore forcing you to do a little analog stick-wiggling QTE to shake them off.
Whether they're Goddamned Bats or Demonic Spiders is down to the individual, but Batman: Arkham Asylum has four up for debate. In approximate order of annoyance, they are: normal mooks with guns, who drain Bats' health like there's no tomorrow; normal mooks with throwable items, who frequently throw from off-screen and hit you out of a combo because once it's thrown, the item's unblockable and the counter window to catch it and throw it back is extremely short and the counter symbol for the item is hard to see due to the speed it's moving at; knife-wielding mooks, who must be stunned before being hit and who have killed many a combo and stun baton-wielding mooks, who can't be attacked from the front period and can stun Bats if he pulls them in with a Batclaw and doesn't get out of the way in time. They're all very annoying in the Story, but it's in the Challenge mode that they take on new degrees of irritation. The worst part is for the trophy-hunters: The fighting challenges require a high score to deliver its prize, and the only way of doing this is not getting hit and not stop attacking. Those guys stun you if you try to stun then, if you try to attack then, and if you try to disarm then with your batgrapple. And the worst of it all is that the baton is on the ground after the prick finally lets it fall off his heand, meaning that every grunt in the room is going to try and grab it. Mostly off-screen. And then you see your perfect score be crushed by a stupid bastard with his recently acquired stun baton.
In the Splinter Cell series, these are usually the various surveillance items. Cameras, motion activated wall mines (of the Flash and Game Over kind) and lasers. None of these (save the aforementioned wall mines), can actually hurt you, but they will wreck your stealth rating and in earlier games could send you restarting the previous checkpoint.
In Splinter Cell Blacklist, this can also be attributed to Drone Operators who send out small drones with red beams of light that will attempt to track the player. While in the Campaign they are rather small with the player only meeting one at a time, the 'survival levels' (Charlie's Missions) will have up to 2-3 Drone Operators around the map with around 6 drones traveling around the map. Cue enemy soldiers already trotting around the environment trying to kill you.
In Hitman (2016), the security cameras on Professional mode. They're hard to see, detect illegal actions, which alarms every guard nearby, and are placed in large numbers in previously safe locations. They're still annoying on the normal difficulty, but they're less of an issue.