In the South Park episode "Human CENTiPAD" Kyle winds up getting more than he bargained for when he accepts the terms and conditions for an iTunes app without reading them. You have to wonder just how easy it would be for something like that (probably with money stealing instead of submission to human experimentation) to happen in real life.
Absurdly easy, but not legally enforceable except in very specific circumstances.
In the first season of Teen Titans, Slade laser-injects nanobots into the Titans. Think about it. Thousands of nigh invisible robots floating around in your body, possibly for decades. And what Slade wanted to use them for is a whole other can of horror.
Are we all going to forget Madam Rouge? She has the ability to stretch with rubber powers, and if that isn't enough, she can transform into anyone she's seen, right down to the clothes and this nearly lead to all the Titans being killed.
In the second season of Legion Of Superheroes, Dr. Londo sent a batch of nanites to infect his son who was asleep at the time and used them to force his son to kill a clone of his to frame his son for his "murder." A few years ago, you thought you were safe after you've escaped your abusive parent who only wants to use you. But not only do they know where you live but they can still control you, and you have no idea that you're being controlled until it's too late.
Dungeons & Dragons: in one episode the villain caused interdimensional portals to appear under kids' beds and his minions dragged them through to perform slave-labor for him — complete with terrified parents trying to keep their kid from disappearing through the rift.
The Rocko's Modern Life episode where the gang goes fishing, only to discover that the fish are fishing for them using ever more elaborate bait, including the life jackets and ending with Rocko's house being reeled in.
The Eye Shock when Filbert "finds" his dive-watch again is unbeatable.
Transformers has any number of Decepticons who disguise themselves as seemingly-innocent objects, from cars to cameras. Only the Sliding Scale of Idealism Versus Cynicism keeps this from being truly chilling, giving us an equally anonymous and omnipresent group of protectors and reassuring us that we can trust them. Rest easy, children. Autobots are watching over you.2007'sLive-Action Adaptation plays it to the hilt with both radio-bot Frenzy and the feral robots brought to life by the All Spark from random machines Sam passed in the street while fleeing the Decepticons... these are better left undescribed. Barricade and Bumblebee probably deserve special mention here, too; the former is a Decepticon who chose a police car to transform into, and the latter is an Autobot who chose an apparently beaten-up ride for Obfuscating Stupidity.
Some of the "Real Gear Robots" in the toyline invoke serious paranoia. Your MP3 player may have been subtly altering sounds so you've misinterpreted everything your friends have said, and your handphone may have been running your phone bill up by itself.
Revenge of the Fallen ups the ante with Alice the human Decepticon. And on the same level as Frenzy is RC-truck-bot Wheelie, but he's a Plucky Comic Relief character. There's also Reedman, a razor-thin 'Con who killed a man by jumping through his torso. Given the right lighting conditions and viewing angle, he's invisible. And Soundwave is up there, listening. Always. In fact, he's probably reading every word you type here.
Soundwave: Nothing moves on the orb below without my being aware of it. I see and hear everything, be it out in the open or behind closed doors. My reach is invisible, intangible. My grip...cast-iron.
Just to make it worse, Reedman was formed from a whole bunch of tiny little pachinko-ball-things that Ravage threw up. This means it can get into anything that has even a pea-sized hole in it somewhere. And you thought regular cat barf was bad news.
The Batman has Ragdoll, a creepy contortionist that can stretch and bend in ways that aren't even imaginable. He once hid in Penguin's hat without being noticed, which indicates he could be hiding in any nook and cranny anywhere.
Fireman Sam. He sounds more like a potential axe murderer than a friendly hero next door. And Postman Pat who sounds more like a Grim Reaper incarnate than a mailman.
Darkwing Duck had a planet of hats. No not like that, a planet full of hat-like aliens who could possess Earthlings by jumping on their heads. And could disguise themselves by simply closing their eyes. We could be in the middle of an invasion RIGHT NOW and no one would know it...
In the truly awful Tom and Jerry: The Movie, practically every single adult the characters meet turns out to be an evil, sadistic monster who cruelly betrays them. (And breaks out into a Villain Song at least once). Great way to turn kids into paranoid freaks, guys.
The Real Ghostbusters and its sequel Extreme Ghostbusters had the Grundel, a ghoul that came to kids' bedroom windows late at night and said "Come out and play..." over and over again in a really creepy voice, until the kid was mesmerized into obeying. And it only targets children. And if they're not freed from his influence, they eventually turn into a Grundel themselves. Sweet dreams, kiddies...
The Brave Little Toaster introduces the concept that every appliance, electronic, or mechanical object is alive, sentient, and watching you. Sure, they are mostly benevolent, but to think that something is always watching what you do, even when you think you're alone...
Dilbert "Do you know how many ways the human body can spontaneously malfunction resulting in instant death?" Seven million.
Invader Zim: The end of the Halloween episode featured Dib getting dragged out of his class, thrown into the back of a padded truck and taken to "the Crazy House for Boys." Think about it. They just decided Dib was insane, with no input from him at all, then picked him up and took him, never to be heard from again.
Actually, that wasn't the end, that was around the middle or so and he escaped.
You're sitting there in your office, and a pale but happy fellow strolls in to ask if he can copyright fish. You tell him no, you know, just doing your job, and for this, you're turned into a smiling, drooling vegetable.
Alternatively, you're driving home on the Highway after an awful day at work, and someone cuts you off. This being the final straw after such a bad day, you drive up next to him, roll down the window, and start into a fit of road rage. Halfway through your tirade, you discover that this man isn't just any random person - he's your city's most wanted psychopath who kills people for the fun of it, and you've just pissed him off. So you try to drive away as fast as you can, and he keeps following you, cutting you off and driving you off the main road. Finally, just when you think you're about to get away, your car runs out of gas and you have no choice but to continue on foot, and so you run into a thicket of trees... only to run right into the psychopath. You plead for your life, saying that you will do anything if he lets you live. He decides he will ask you a favor at some point in the future, takes your Driver's liscence and the information it contains, and lets you go. Terrified he'll find you again and really not wanting to know what he'll do when he finds you, you and your entire family move to another state, change your names, and stay in hiding. 2 years later, despite all of these precautions, you get a phone call, and it's from the same psychopath. How did he find you? Oh, he never lost you. And he wants his favor.
The end of "If You're So Smart, Why Aren't You Rich?" shows that even though Batman saved him from The Riddler, Daniel Mockridge has been reduced a paranoid wreck, who sleeps with his gun, and checks every nook and cranny in his house before going to sleep.
Batman: How much is a good nights sleep worth? Now there's a riddle for you.
Generator Rex. In this world, nanites have invaded every living thing. It just so happens that when a particular thing gets overloaded with nanites, it causes the body to mutate in very squicky ways, eventually causing it to grow into a giant monster striving to destroy anything in its' way. Which means that a) for example, your cat, the grass in your backyard or one of your symbiotic bacteria could turn into a rampant beast at any moment and kill you, b) your body could start mutating any second, undoubtedly causing much pain if the agony-filled screams of things that got overloaded with nanites are anything to go by.
If it's the latter, use what may be your last few seconds of being you to pray that you're curable. Not everyone gets that luxury.
Season 2's Discord knows way too much about the mane cast in spite of the fact that he's spent the past millennium in stone.
Changelings. They masquerade as a loved one and feed off your love, slowly draining you and making you weaker and weaker, all the while making themselves stronger. The powered-up Changeling Queen was able to defeat Princess Celestia.
Mayor Jones' big reveal to Freddie in the 26th episode. The man who calls himself your father isn't really your father. He kidnapped you as a means to blackmail your birth parents into never returning to their hometown again, so he can search for a treasure that no one is sure even exists. Everything he's ever told you about your life? It's a lie.
In the Sequel Series, The Legend of Korra, Amon and his Equalists launch an actual terrorist attack on a sports arena, which is already horrific given the family-friendly nature of the show. Right before the attack begins, the noise level goes down and you see all the members of his group, just random people in the arena crowd, slowly start putting on masks and reaching into popcorn bags to pull out weapons and bombs they snuck in, and then proceed to incapacitate every cop in the arena before they even know what's happening.
Lub Glubs. Innocent, harmless pool floaties could be a disguise for an Eldritch Abomination that are nothing more than a shapeless mass of darkness and what appears to be a mouth filled with teeth. A lot of teeth!
The Ice King's backstory as well. Basically, he was just a normal guy until he jokingly put on a normal-looking antique crown that he had bought. Said crown turned out to be enchanted, causing him to drive away his beloved fiancee, destroying his mind and identity slowly over a period of years, and all-around ruining his entire life.
In the King of the Hill episode "Gone With The Windstorm", Bobby is constantly being tormented by a bully who pops out of weird places (like Bobby's locker and the lunchroom conveyor belt). When Hank decides to deal with the bully's father, he discovers he's one of his victims!.
Father: Watch out when you pass the mailbox. That kid can wedge himself into anything!
The Gamesmaster from the G.I. Joe episode of the same name. A ten-foot tall Psychopathic Man Child who effortlessly kidnaps Flint, Lady Jaye, Baroness, and Cobra Commander to use as playthings for his amusement. It's insane that such a creepy guy has so many resources. The Joes and Cobra already have Surveillance as the Plot Demands, but he takes it to the next level as he spies inside Cobra's base, Lady Jaye changing her clothes in a mall's fitting room, and Baroness taking a bath. He kidnaps Flint by using a helicopter to pull the elevator he was using out of the building.
The PSAs for the 1985 G.I. Joe series can be Paranoia Fuel when you think about it. There are AWOL soldiers (and military personnel) who randomly appear out of nowhere to give advice to stupid kids. Then there is one where two boys are swimming and a lightning storm is about to come their way. One of the boys stays behind, but is forced out by Deep Six (an underwater operative in a bathyoscopic suit) who, apparently, has been underwater this whole time for no reason other than to spy on little boys in their swimming trunks.