In order to defeat Telepathy, frequently all a character has to do is fill their mind with something useless. This can take several forms. Often mentally reciting nursery rhymes or acquiring an Ear Worm will do the trick. Sometimes characters use especially compelling fantasies; conversely, sometimes they deliberately force their thoughts to be as mundane as possible. An especially Badass and unscrupulous user can fill his mind with Mind Rape thoughts (or just bad memories of very horrible events from their life) in order to repel anyone trying to read it. In any case, the goal is to drive out whatever thoughts they don't want the telepath to know about.
This trope often provides a way for Muggles and Badass Normals to get the upper hand on characters with Psychic Powers. However, it's usually implied that keeping up an effective screen of Psychic Static requires a heroic level of mental discipline: otherwise, the telepathy wouldn't ever be useful in the first place.
One of the ways a character can give someone a Poke in the Third Eye. For a defense that's always on, see Psychic Block Defense. For madness working this way, see Insanity Immunity.
Occasionally, a psychic or a normal may need to evade a telepath using Psychic Radar to scan for the presence of sentient thought. Depending on the situation, the mundane thoughts trick may let them blend in amongst the minds the Radarpath expects to find. Sometimes they may have to employ more extreme methods such as blanking their mind or thinking thoughts that make them seem like an animal mind.
Often overlaps with the Jedi Mind Trick, but is generally more passive.
In YuYu Hakusho, Yusuke was able to beat Murota's "Tapping" ability by repeating the way he planned on punching him over and over in his head, and then knocking him out just through the reverberations from his fist in the air. Subverted later on; Kurama defeats Gourmet-using-Murota's-Tapping ability by attacking in a blind yet Tranquil Fury; in other words, he defeats Gourmet because he has no thoughts to read. But Elder Toguro is using Gourmet using Murota, and Kurama doesn't do anything special to hide his thoughts, yet manages to trap him in the Janenju tree. Itsuki speculates that, since Kurama is Really 700 Years Old, his mind is too ancient and layered for something like Tapping to even scratch the surface of it.
Attempted (and failed) in one episode; the psychic in question even compliments the protagonist for having had the idea to do this in the first place, but then focuses harder and is able to pick out his real thoughts.
In the previous episode, the hero pulls a variation by sending a large number of policemen after the psychic; since he can't shut off his power, this is much more successful.
Attempted with moderate success in One Piece. Luffy shuts down his brain and acts purely on instinct in an attempt to sidestep Eneru's telepathy. While this does allow him to dodge anything thrown at him, he's unable to mount any sort of attack.
At one point in the manga Ray, the title character asks a telepath she's just saved to see if he can read her mentor's mind. He can't — wherever he tries, the mentor switches his thoughts to a game of shiritori.
At one point in Fairy Tail, Natsu was confronted with an opponent whose hearing was so good he could literally hear thoughts. Cue Natsu not thinking at all.
One episode of Lupin III features a telepathic villain who can use his ability to avoid attacks. His killer kept the guy out of his head by whistling.
Similar to the Carpe Juguluum example below, being drunk allows humans to see through the illusory human forms of Wolf's Rain's wolves.
In one chapter of Zettai Karen Children Minato uses the 'Riemann hypothesis' for this, concentrating on the complicated mathematical formula as a psychic defense against a mind reading middle schooler.
Happens by pure accident in Flame of Recca when Domon's opponent (who was wearing a rather Stripperific outfit because of the heat, not because she was an exhibitionist) suffers a wardrobe malfunction and all Domon can think is "BOOBS BOOBS BOOBS". This freaks her out big time.
In episode 7 of Kotoura-san, Manabe plans to hold a Surprise Party to his girlfriend and local telepath Haruka. He hides that thought from her by using multiplication tables, and, at one point, Mouthful of Pi.
In an issue of The Avengers, Ultron was thwarted when he attempted to read a disguised Hank Pym's mind when The Wasp hypnotized him so that his subconscious would be filled with the phrase "thou shalt not kill". The concept was so foreign and confusing the the killer robot, it managed to stun him.
Rogue of the X-Men was originally stated to have automatic Psychic Static created by Carol Danvers' absorbed psyche, making her mind impossible for even Professor X to read. This apparently fell by the wayside even before Carol's psyche was removed from Rogue's mind.
Also in the X-Men comics, Gambit has been known to employ the intentional version, at one point revealing to several Xavier Academy students that he pictures The Blob naked in order to make sure that telepaths like Rachel Summers and Emma Frost aren't eavesdropping on his thoughts. Under some writers, his passive empathy secondary mutation acted as literal psychic static that rendered him invisible to psychics.
Wolverine too, due to the monkeying that Weapon X did (for precisely this reason) to his brain patterns, coupled (possibly) with the way in which his healing powers work to ameliorate his painful memories. Same goes for his son Daken, only it's more lethal.
Storm has a literal static mind because of her weather powers.
In New X-Men 130, a soldier warns Xavier that all he'll see if he tries to read his mind is "re-runs of the adult channel". Xavier learns the hard way that he's not joking. Apparently, learning to put up Psychic Static is part of that military's training.
Also interestingly inverted in another issue of New X-Men. Jean Gray has the Beast think of "a pink door opening" in order to more easily access his medical knowledge.
In Stormwatch: Team Achilles, the Mind Probe of Senator Sonny Terns eventually succeeds, but due to the senator's Mind Rape thoughts, the telepath is the one traumatized by the experience.
Deadpool's mind has been stated as being too chaotic to read. His rival/friend/heterosexual life partner Cable once burned off overcharged psychic powers by going into Deadpool's mind, because the effort would wear him out.
Doc Samson is shown to keep all his gamma fueled rage locked up in his mind to unleash on psychics looking to get into his head.
The original Gamma hero The Hulk can do this too.
Grant Morrison introduced the villain Prometheus during his run on Justice League of America. Among his talents was the ability to introduce 'neural chaff' into the minds of his opponents, making it difficult for them to concentrate. This didn't work on Captain America during a brief encounter in Book 4 of JLA/Avengers. As Cap observed, "Try fighting the Wehrmacht. Teaches you focus."
When Nextwave faced off against the ridiculous-looking but intensely powerful Forbush Man, he lifted his pot-helmet and sent all of them on a mental journey into their worst nightmares. All of them, that is, except one, who was just too air-headed for the power to work on.
The psychics who have survived reading The Joker's mind have reported various unsettling things, such as nonstop insane laughter, screaming, a labyrinth of funhouse mirrors, incredibly detailed descriptions of past murders, a vast battle between bat and clown faced demons, "a billion fiery locusts blotting out a dead black sun", and Three Stooges reruns.
It was revealed after the "Tower of Babel" arc that Batman developed his counter-measures against the League, and J'onn in particular, by actually burying his memory and restoring it with a series of mnemonic triggers when he wanted to work on his plans, and instructed the computer to track J'onn and "activate the burial key" should the Martian come within 100 miles.
Nobody Dies had Iruel trapping everyone in a virtual reality sim under his control. When he looked into Rei's hallucination, however, he witnessed Rei getting it on with Unit 05 while surrounded by their Spider Tank children.
One Stargate Atlantis fic has a brilliant in-character example. What does Sheppard use to fend off a Wraith queen's mind probe? Singing Johnny Cash in his head. Hilarious because it is canon that Sheppard likes Johnny Cash, as evidenced by the poster hanging above his bed in numerous episodes. The queen is like, "what the hell is this bullshit?!"
Happy Flame Time's TouhoudoujinFly Up from the Underground, has series protagonist Reimu use two different tactics against Satori. The first involves thinking of a story that doesn't go anywhere, while the second is a parody of the Yu Yu Hakusho example, with the defeat coming when Satori is distracted by the "and take off all her clothes" bit Reimu adds to her attack plans.
The Doctor Who fanfiction Night Terrors (not to be confused with the episode) has the Doctor teach Rory how to "shoot" bad thoughts at beings who try to possess him as a defense mechanism.
With Strings Attached has a variation on this trope: Ringo experiences great pain whenever he tries to scry the Ghost City of Ehndris, thanks to the Poison Protections maintained over the city. Later, when the four go there, the Poison Protections keep him in constant, massive pain and effectively neutralize him until he accidentally teleports out of the city.
When Professor X tries to read Lance's mind in "After Hours", the only thing he gets is an endless loop of "My Humps". Which Lance also sings later when being interrogated by Nightwing.
In A Study in Magic, Sherlock Holmes does this accidentally to anyone who tries to read his mind. He thinks too fast for anyone else to follow. He later reveals that they're "slowing [[his]] thought process to an agonizing crawl". Yes, for Sherlock, thinking too fast for anyone to follow is slow.
Eugenesis states that Soundwave, for whatever reason, cannot read Galvatron's mind (Probably because Galvatron is insane). He can tell it's there, but he can't read it. This is how he figures out Galvatron's gone missing, as well.
Apparently somewhat common in A Third Path to the Future. Storm's powers offer a passive defense that make accessing her mind difficult. Jean's mind is surrounded by tentacled trees. And Harry's mind is completely impossible to sense unless he allows it.
In Walking on Sunshine, Xander has a mental barriers based on the feeling of the split second before an orgasm. Emma Frost tries to read his mind and orgasms so hard she passes out.
Films — Animated
The Flight of Dragons: Sir Orrin Neville-Smythe and Peter Dickinson sing to to push back the suicide-causing noise of the Sandmirks.
Peter: "I come from Alabama with a banjo on my -AAAH!"
In the original version, the protagonist is able to temporarily neutralize the creepy kids' telepathy by imagining a brick wall. Literally.
In the 1995 remake, he thinks about the ocean very intensely to stop the psychic alien kids finding out about the explosives that he's rigged to destroy them.
In Flash Gordon (1980), Dr. Zarkov beats Ming's brainwashing machine by throwing every irrelevant memory he can at it — Einstein's formulae, passages from the Talmud, and Beatles songs — and then faking the desired effect for his captors.
Attempted and failed in the first Ghostbusters film. The ghost busters have to "choose the form" of their destroyer by imagining it. They try to clear their minds, but all Ray can manage is to think about things that should be totally harmless. The Stay Puft Marshmallow man is not so harmless when made as big as a skyscraper, though at least it was reasonably defeatable.
Subverted in the Fighting Fantasy book Rebel Planet; doing this just gives the evil alien easier access to your mind. The correct defense is to clear your head.
A Magic: The Gathering book has a character envision a large mental fortress that the invading psychic had to break into.
"Tenser," said the tensor. "Tenser," said the tensor. "Tension, apprehension, and dissension have begun."
Although that works only on 3rd and 2nd Class Espers. For the protection from the strongest, 1st Class Espers (one of which is a Police Prefect), the protagonist has to bribe and employ a 1st Class Esper of his own.
The short story "The Foreign Hand Tie" by Randall Garret also uses this.
In Chrome Circle by Mercedes Lackey and Larry Dixon, Tannim the mage fends off Elven mindreaders this way (to their distinct distress) using They Might Be Giants songs, including "Put Your Hand Inside The Puppet Head", "Birdhouse in Your Soul", and "We Want a Rock". One of the telepaths is reduced to incoherent gibbering before they drag it away.
In The Dragon And The George, James Eckert goes over his master's thesis in his head to push back the suicide-causing noise of the Sandmirks, while Sir Brian recites prayers.
In A Wrinkle in Time, Meg tries to hold off IT's mind control by mentally reciting nursery rhymes and the periodic table. It works initially, but IT overwhelms such efforts later on and must ultimately be defeated by the Power of Love.
In one of the The Dark Is Rising books, Will prevents a villain from reading his mind by thinking hard about his breakfast.
There's a variant in the short story "It's a Good Life", by Jerome Bixby (as well as the The Twilight Zone episode based on it). They feature people constantly mumbling songs — not in order to keep the omnipotent child from looking into their thoughts, but so they won't think of anything unbecoming.
This is supposed to work on vampires' mind reading and control. Carpe Jugulum mentions that vampire hunters often work completely drunk, and that the vampires can't influence Agnes' mind due to interference with the thoughts of her alter ego, Perdita.
Rincewind manages to keep the Elf Queen from learning about his scheme to defeat the elves in The Science Of Discworld II until it's too late to stop it by obsessing over potatoes whenever she's in the area.
Asimov's novels feature the Psychic Probe, a machine which can read minds, and while it's apparently possible to defeat one this way, it's a very bad idea that can result in amnesia and permanent brain damage. An electric static field, however, works perfectly.
The Foundation series creates a device with this effect, the "Mental Static Field", to elude the telepathic Second Foundation. When used at high power, the device also doubles as a weapon against telepaths. Of course, the Second Foundationers anticipated the creation of the device, given the First Foundationers' concerns about being controlled. The whole thing was set up in order to trick the First Foundationers that they have discovered the location of the Second Foundation and neutralized them all (sacrificing 50 members in the process). Thus, the Mental Static Field would be rendered useless and, eventually, forgotten, allowing the Second Foundation to do its thing unhindered. It works, although the device is later restored through archived plans and used again.
In the Inheritance Cycle, you can block someone from entering your mind by concentrating solely on one thought. Unfortunately, it is impossible to tell if someone has done so unless you are telepathic yourself. In Eldest, it is revealed that a number of important figures have trained themselves to do this all the time without any hindrance.
Eragon attempts to keep someone from entering his mind by concentrating on his big toe. Other characters often use similar techniques, with varying levels of success.
In Fingerprints, a psychic with the ability to inflict Laser-Guided Amnesia and implant Fake Memories tries to hide a crime from a mindreader by implanting lots of "witnesses" with contradictory fake memories about the event.
In The Redemption of Althalus by David and Leigh Eddings, it is possible to prevent mind-reading by counting in your head, and mixing up the numbers intentionally. The villain's designated mind-reader hates this. A lot. Taking this a step further, fractions are actively painful to the reader.
Tanalasta quickly chased from her thoughts all memory of the vision itself, instead picturing Merula the Marvelous trussed naked on a spit and roasting over a slow fire. If the wizard was spying on her thoughts, she wanted him to know what awaited if he dared report any particular one to the royal magician.
In R. A. Salvatore's Forgotten Realms novels, Jarlaxle uses a similar tactic on the psionic Matron K'yorl of House Oblodra. In this case, naughty thoughts irritate the Matron intensely, and mind-reading is frowned on in Menzoberranzan.
A variation in the Animorphs books: Humans who have been infested and taken over by Yeerks can't really do anything to stop the Yeerks from reading their thoughts and hijacking their brains, but they can still annoy the hell out of them. Visser Four's host was a failed actor who nevertheless memorized William Shakespeare's Henry V and recited it constantly — to the point where the first thing Visser Four does when he gets his hands on the Time Matrix is go to the Battle of Agincourt and try to kill the inspiration.
The Black Magician Trilogy: Sonea tries this against Akkarian when he mind rapes her, throwing random images at him. He just gets impatient and forces her to stop
In the Vorkosigan Saga, a not-quite example comes when Miles is subjected to fast-penta, a drug that makes you tell the truth (analogous to having your mind read). Typically, he doesn't react normally to the drug, gets even more hyper than normal, and can't stop talking (that last one a normal fast-penta result). So he recites Shakespeare. For about four hours.
In Angry Lead Skies, Garrett verifies that the silver elves (all right, the aliens) are reading his mind by imagining an X-rated encounter between himself and one of them, then seeing her flinch in response.
In Donovan's Brain by Curt Siodmak (and the movies based on it), a character puts off the mental influence of the title Brain in a Jar by repeating an inane rhyme in his head.
The same rhyme is later used for a similar purpose in Stephen King's It. This is an intentional Shout-Out. King had singled the scene in Donovan's Brain out for praise in his nonfiction book Danse Macabre.
In the Twilight series, Alice keeps Edward from reading her mind by translating a book in her head. This isn't as much to protect her secrets as to keep him calm — she told him what she was hiding later.
In the book Dead Beat, Harry is under psychic assault by a necromancer named Corpestaker, who is trying to pry the location of a book out of Harry's head. Our hero pictures a granite wall separating his mind from hers, which he infuses with his power like he was trained to do. This blocks Corpsetaker out... until she actually starts trying. Then Harry's fighting a losing battle to keep his wall intact as the necromancer places it under an enormous, steady psychic pressure.
"Delicious," Corpsetaker said, and her voice didn't sound strained at all. "After a century, they're still teaching the young ones the same tripe."
After tapping in to Hellfire to patch up his wall, Harry manages to escape for a minute or two — until a Ghoul throws a shuriken into his leg, breaking his concentration. After Corpsetaker successfully gets into his mind, Harry stumbles in such a way that the shuriken twists in the wound, driving her (him?) out through pain feedback.
In Ghost Story, it turns out that the White Council has stepped up their defensive training, resulting in much more elaborate constructs and culminating in a full-on Battle in the Center of the Mind.
In C.S. Friedman's The Wilding, the supposedly badass and dangerous female psychic is handily defeated by the Anti-Hero imagining himself raping her repeatedly.
In the Tunnels series, Will's mother is able to resist the Dark Light by reciting the litany, "I pray that I might not let those about me spoil my peace of mind". Unable to get anything out of her, the Styx turn the device up to the "Mind Rape" setting and destroy her consciousness instead.
In Stephen King's The Tommyknockers the protagonist, Jim Gardener thinks of "old addresses, bits of poems, snatches of songs", or just repeats the word "shield" to hide his thoughts.
Subverted in a Russian short story, where a "reader" is talking to a scientist. He mentions another young scientist who keeps trying to block him out by reciting complex physics formulas in his head. The reader simply says that, while he has no idea what all those symbols mean, he does have a pretty good idea about how the guy feels about a certain young female assistant.
In Jack McDevitt's Alex Benedict series, Alex is able to shield his mind from the telepathic Ashiyyur by obsessively focusing all this thoughts on the price of various antiques (he is a dealer in antiques, and very passionate about his work).
Mind-blocking is common among the Kindar in the Green-Sky Trilogy. It's used to prevent others from reading your thoughts and finding out you are having forbidden "troubled" or "unjoyful" feelings. A sign of the society's deterioration is the high amount of mind-blocking that goes on even between friends and family members. It's never said openly, but this is one of the reasons for the loss of once common psychic abilities.
In the Firebird Trilogy, this is the only way for a non-telepath to defeat a telepathic Mind Probe, usually in the form of concentrating on something uninteresting and irrelevant, such as boot heels.
In a StarCraftExpanded Universe novel, a crime lord picks a fight with an unregistered telepath. He recruits a large number of drug addicts near his compound to confuse her and hide his mind shield device until it's too late.
Arcturus Mengsk could make his mind difficult (but not impossible) for a telepath such as Sarah Kerrigan to read. In the Frontline manga, Corbin Phash was trained by his six-year-old telepathic son to keep his thoughts hidden, which could hide him from a (weak) telepath.
Subverted in the Emily The Strange novel "The Lost Days": Emily tries this to prevent a child psychic from uncovering crucial information and passing it on to his employer, who is her enemy. She uses a thought amplification device on her cats (to make their thoughts louder) and brings them with her to meet the psychic, hoping that the cats will drown out her own thoughts. It seems to work, but the psychic later sends Emily a letter revealing that he knew what she was up to the whole time. He can't read the thoughts of animals, so he was aware of every thought she had during their meeting. He just didn't pass it on to his boss because he considered Emily a friend.
In the Relativity story "August Moon", several of the heroes need to fight a powerful telepath, and each comes up with their own type of psychic static to stop him from reading their minds: The Dark Flame concentrates on nursery rhymes, blocking out all other thoughts. The Black Torrent thinks normally, but thinks all of his thoughts in Arabic. (He had used Portuguese at first, but that turned out to be a language the villain knew.) And Overcast unintentionally slows the villain down with happy memories from before he became a villain.
In the episode "A Race Through Dark Places", a captured telepath tries to block Bester from reading him by reciting "Mary Had A Little Lamb". (Since everything ESP-related in Babylon 5 comes from The Demolished Man, this is unsurprising.)
Later, an assassin tries to kill Garibaldi. When he's captured, Garibaldi gets Lyta to mind probe him. He resists by singing and doing math equations in his head, but since he's essentially taking on the telepathic equivalent of a WMD, he lasts... ooh.. less than 20 seconds. And that's only because Lyta takes some time to screw with him.
In addition, human telepaths are trained to do this to themselves since their powers don't have a convenient off-switch to ensure they don't accidentally read the minds of everyone in the room. Which of course they would never do deliberately.
In another situation with Garibaldi, he and several other people are attempting to avoid a group of telepaths, and he tells them they're headed to a dock. Since they're frightened and panicked, the telepaths immediately pick up this thought and head there themselves, while Garibaldi instead takes them to another section without letting them know; being calm and collected, his own thoughts (and the real destination) are nearly impossible to pick out of the crowd of panicked people following him.
The first pilot episode has Captain Pike being held captive by a race known as Talosians. Pike works out that aggressive, violent thoughts would keep the Talosians from interfering with his mind.
An episode of Star Trek has a villain making a robotic duplicate of Kirk, who focused on racist thoughts about Vulcans during the procedure — so that Spock would know that something is wrong when the duplicate would insult him over every trivial thing.
The Star Trek: The Next Generation episode "The Survivors" has a proactive variant of this trope: a character projects music-box music into Troi's mind to prevent her from figuring out that he's an alien.
It's also worth noting that for whatever reason, Ferengi are completely unreadable to telepaths.
An episode of Star Trek: Voyager has a psychic trying to forcibly take violent thoughts from Tuvok to be sold on the black market of a planet of pacifists. Tuvok managed to overpower him by concentrating on his very worst, horrific thoughts.
A variation occurred in an episode where Tuvok, Janeway, and Torres got themselves assimilated by the Borg deliberately as part of a plan (with precautions taken to keep them from being absorbed by the Collective). Tuvok, whose protection wore off much faster, had to recite details about his own life and experiences (particularly memories of his family) to keep his individuality intact. The Borg Queen eventually got to him, but by then their plan had succeeded and all three were rescued in short order.
Jo does this to the Master in Doctor Who, resisting the Master's hypnosis by reciting nursery rhymes. The Master gives up in simple annoyance.
Mr. Bennet thinks in Japanese to throw off Mindreaders, specifically Matt.
Angela is also able to stop mind readers, mostly through sheer strength of will, and told Matt to "Stay out of [her] head", mentally. However, if Matt tries hard enough, she will give in involuntarily and get a Psychic Nosebleed.
This has also been done with Peter and Matt. It seems to be a general rule in Heroes that trying to read another psychic results in some pretty painful feedback. However, this may just be because they both were trying to read each other's mind at the same time, kind of like putting a microphone next to a speaker.
Played absolutely straight in an episode of Sliders, when a villain tried to download Quinn's brain into an android. All the android got was one of Rembrandt Brown's songs.
In the season 1 episode "Sparks Fly Out", Tara doesn't want telepath Sookie to read her thoughts, and when Sookie tries all we hear is "LALALALALA..." The wide-eyed look of intense-focus on Tara's face as she does this make this hilarious.
In the first season finale, Sookie is with Rene, the killer. She keeps trying to read his mind, and he keeps reciting "Don't think, don't think, don't think...". He eventually slips up though having a flashback of him killing Sookie's grandmother.
Battlestar Galactica (1970's) episode "War of the Gods Part 2". Commander Adama needs to prevent Count Iblis from reading his mind and finding out where Apollo has gone. He plans to shield his mind by crowding it with other thoughts, a technique he learned at the Colonial Military Institute.
In The Avengers episode "Too Many Christmas Trees", Steed and Mrs. Peel come under psychic attack. Their defenses include "Green Grow the Rushes, O" and an obsession with socks.
Daphne in No Ordinary Family tries to read Joshua's mind but ends up literally hearing only static. This freaks her out and makes her suspicious of him.
The Outer Limits TOS episode "The Mutant". A scientific expedition on another planet is under the control of the title creature (a former human) who can read thoughts. One of the expedition members tries to get a note to a recent arrival to warning him of the danger. When the mutant tries to read his mind, he tries to hide information by thinking about how he misses dreaming. Later on another character thinks of a riddle for the same purpose.
1960's Batman episode "An Egg Grows In Gotham/The Yegg Foes In Gotham". Egghead uses a machine to try to transfer Bruce Wayne's memories to himself so he can learn if Wayne is Batman. However, he only gets trivia from Wayne's mind. Later, Wayne explains explains to Dick Grayson that years of mental conditioning allowed him to block off access to the part of of his brain pertaining to his dual identity. This left only the trivial contents of the rest of his mind (his "Bruce Wayne" identity).
In the Stargate Verse, human-form Replicators can read a person's mind by literally sticking their hand in the person's head (technically they are sending nanites through the skin and into the brain, but details). In Stargate Atlantis, an Asuran Replicator is surprised when O'Neill, who's been on the receiving end of this a few times, is able to resist the intrusion and hide his thoughts.
On The Listener a number of people have been able to inadvertently mess with Toby's telepathy because their brains don't work like those of most humans. A genius criminal was thinking so fast that Toby was getting a jumble of a dozen different thoughts. A man with eidetic Photographic Memory remembered everything in such a great detail that Toby was overwhelmed by information overload. A newspaper reporter has epilepsy and the medication she takes for it has the side effect of blocking telepathy. In general, Toby can only read surface thoughts so he needs to prompt and trick other people to think about the information he needs. People who know of his ability can thus trick him by thinking about other subjects or thinking about things that are not true.
Destroy The Godmodder: Subverted. One player decided to make a joke by "reading the godmodder's mind" and coming out with a picture of a tuba. TT2000 rolled with it and it ended up being and actual weakness.
The Tyranid Hive-Fleets project the Shadow in the Warp, created by the psychic disturbance caused by the Hive Mind, cutting off interstellar communications (which are the duty of telepaths). The Shadow doesn't usually kill psykers directly, but rather causes them to go insane, ramble about hundreds of chittering voices coming from inside their heads and then kill themselves.
Coincidentally, the dying screeches of Tyranid synapse creatures in Dawn of War II overlap with the sound of radio feedback, and the Mind Rape cutscene that introduces the Zoanthrope similarly features a lot of static or feedback noises.
In GURPS this skill is called Mind Block. In fact, the Gurps SupersSource Book adds three variants: "Coded Thoughts": thinking in code, "Camouflaged Mind Block": hiding behind fake surface thoughts (which also hides the fact that you're hiding your real thoughts), and "No-Mind": rendering yourself completely invisible to telepathy.
Certain creatures have this as a natural ability. In the Ravenloft setting, trying to read the mind of certain things (including such "mundane" things as pretty much any non-humanoid-type creature) will drive you insane.
Eberron has the Daelkyr, who will drive anyone who tries to read their mind stark, raving mad. Most of their creations, especially Mind Flayers, have a lesser variant.
In 1st and 2nd Edition the psionic defense mode Mental Barrier "is a carefully built thought repetition wall which exposes only that small area."
The 2nd Edition Complete Psionics Handbook allows a non-psionicist to resist the "Contact" devotion with a barrage of thoughts and emotions. This only cause a meager penalty on the psionicist's roll, however, and the resisting character cannot do anything else.
Rogues can gain abilities like "Slippery Mind" in the 3rd and 4th editions, which make them resistant to mind-affecting abilities including mind-reading.
Fiendish Codex II has a Prestige Class called the Hellbreaker. At level 1, it gets this in aura form as a class feature.
The Ordo Dracul from Vampire: The Requiem have developed a technique where this is done automatically, straddling the line between Psychic Static and Psychic Block Defense. The vampire splits his consciousness in two, and any attempt to intrude upon his thoughts is redirected into one half of his mind, which is playing a constant, closed loop of thought, which can be anything from circular internal monologues to memorised statistics to "disturbingly elaborate dismemberment visualisations", or even something as simple as a constantly repeated mantra — such as "Fuck you, you can't read my mind".
It became common practice at Bradford by Night, a LARP version of Vampire: The Masquerade, to combat the higher levels of Auspex by musing "Wouldn't the Prince look lovely in a gold lamé suit?" or "White Rabbits, White Rabbits, White Rabbits."
Traveller, Journal of the Travellers' Aid Society #14. The "Casual Encounter" for this issue is Lothario Lochinvar Finger. His mind cannot be read: anyone who attempts to do so gets a stream of trivia (disconnected vidphone numbers, porkbelly futures prices, who played the Lone Ranger on TV).
In Exalted, users of the Infernal Monster Style can learn a charm that makes any divinations around them fail, causing them to return only "The monster is here."
In Knights of the Old Republic 2, there's a long, multi-planet dialogue tree to figure out how Atton blocks telepaths by playing space-blackjack in his head. And why. It also reveals Jedi killers would "throw up walls" of strong emotions such as lust or rage to mask their true emotions. Ironically in many cases with the proper training the less force sensitive an individual the greater their ability to mask their intentions from Jedi could be.
According to Kreia, she cannot read Bao-Dur's mind due to aliens thinking in their natural language and thus requiring translation. She's somewhat dubious when the Exile reveals that they can sense his thoughts, due to their close bond from serving together in the Mandalorian Wars.
This could be why Bug-type moves are super effective against Psychic-types; their brains are too small (or possibly too dispersed) to read.
In a similar vein, this is one theory why Dark-types are flat-out immune to Psychic damage — either their thoughts are just difficult to follow, or prolonged perusal is next to impossible without severe trauma.
This is supported by the fact Dark-types are literally called 'Evil-types' in the original Japanese version. Their thoughts could just be too vile and malevolent for a psychic Pokemon to handle (see: the Dark-type move 'Nasty Plot'). Dark/'Evil'-types are named so for their knack at fighting dirty, so it could also be they use their cunning to create a form of psychic static (annoying songs, disturbing fantasies, thinking of nothing etc.).
The novelization of Halo has Captain Keyes make a Heroic Sacrifice by surrendering his personal, but strategically useless memories to the Flood. He also kept giving them his name, rank, and serial number which was generated by the chip in his head, so it didn't get destroyed like his other memories.
In System Shock 2, when you create your character, you choose the branch of military he enlists in, then the missions he took part in before the game starts. One of such missions for OSA (telepathic special forces) agent includes capturing an assassin who tries to hide her own intentions under "quite explicit daydreams".
It's mentioned occasionally in Golden Sun that Adepts can detect their minds being read, and react against the reader. The best example of Psychic Static in particular is a cutscene where Ivan demonstrates his Mind Read powers on Garet, who is thinking, "Stop reading my mind, Ivan!" and nothing else.
In the third "season" of Sam and Max games by Telltale Games, Max gains the ability to read minds, but some characters are immune:
Girl Stinky scares Max out of her mind by thinking about shoe-shopping.
Agent Superball regrets to inform Max that the contents of his mind are classified.
In Star Control 2, it is revealed that the Dnyarri feel some measure of what the people they are controlling feel. This creates a disturbing but effective countermeasure to their mind control: constant, excruciating pain. No wonder the Ur-Quan are so screwed up.
In Grand Theft Auto: San Andreas, The Truth convinces CJ and co to "Think of a pink golf ball" and other such oddities when you reach different locations. He doesn't say WHY he says to do these things, but it's presumably to make sure CJ doesn't think that he's avoiding a mind-scan, which would tip off whoever is reading your mind that you're trying to avoid having your mind read.
In The World Ends with You, there are a few random Non Player Characters who are latent psychics and can detect your use of telepathy. If you use it on them, their thoughts will simply reveal a scolding for trying to read their mind.
In Sid Meier’s Alpha Centauri, the native life attacks you psychically. You can capture or breed and control the life, or (later) technologically mimic its effects and use them as weapons of war for your own ends. The movie for the Dream Twister Secret Project seems to indicate that one of the techniques (failed in this case) to block the attacks is this trope.
In another example, Dr. Schlock evades a vampire's mind-reading abilities through sheer vocabulary. Note that in this case, the vampire does actually see what Dr. Schlock is thinking; but cannot understand a word of it.
In When She Was Bad, Jasper prevents Gail from reading his thoughts by thinking about the Mario Bros. theme song on a loop.
In a Narbonic non-canon fan story, Helen manages to break a psychic foe by wandering into a perfectly white, featureless room and letting her madness run away with her. Gazing into the head of a Mad Scientist is not a good idea for the terminally sane.
When rich kid Phase is getting powers testing, s/he tries this against powerful telepaths by concentrating on stock market analysis. It doesn't work all that well.
In a much later story, Phase quits on the stocks and goes with a Britney Spears song that has the psychic begging him/her to stop.
Eldritch, on the other hand, has turned her brain into a psychic minefield, and makes anyone who attempts to intrude experience gunshot wounds and other injuries she suffered in the past.
In a Whateley Universe fanfiction, Caroline White, a healer, suffers from this after the MCO produce a device (or, more likely, a devise) which generates massive amounts of artificial pain. It eventually sends him into seizures.
In Worm precogs' ability to sense the future is interfered with by other precogs, hence why their predictions haven't destroyed the economy (with government employing thinkers and precogs to counteract them).
On Justice League, Batman keeps John "Dr Destiny" Dee out of his head by humming "Frčre Jacques" and drinking lots of coffee (to keep himself awake, since Destiny could more easily get into the mind of a sleeping person). Also of note is the fact that Batman was a complete jerk about this victory, repeatedly taunting Destiny about his inability to get in Batman's head after the rest of the League was incapacitated. This may have been the only time Batman actually taunted a villain (it was for good reason; he needed to rile up the bad guy to disrupt the psychic's ability to get in his mind). And doing this after having already been up 3 nights straight.
Batman: Whaddya say Johnny? Wanna go one-on-one? It'd give you something to brag about.
In Young Justice, Bane resists Miss Martian's telepathy by reciting Spanish fútbol scores in his head. This is a semi-common skill in the show's universe — Professor Ivo scoffs "As if I've never faced a telepath before!" when she tries to read his mind in a later episode. Miss Martian can break through these kinds of things (one of her skills is, in fact, translating other languages directly to your brain), but it takes a lot of effort, isn't pleasant if you resist, and she can't really read a mind in-depth without cluing the person that she's in there.
Freakazoid!: To avoid having his personality stolen and fed into his clone, Freakazoid keeps thinking of his favorite show, Hero Boy. This causes a bunch of evil Hero Boy clones to appear. But since these are clones of Hero Boy, a very ineffective superhero, they were easy to subdue.
Inversion in an episode of The Fairly OddParents: Timmy gains the power to read minds, with the disadvantage that it is not selective. When Mr. Crocker tries to use a group of kids to overwhelm Timmy with thought, Timmy is able to find Cosmo and Wanda in a group of green and pink objects by hearing Cosmo's mind — elevator music.
Mentok tries to read the mind of washed-up motorcycle daredevil Ernie Devlin in an Episode of Harvey Birdman, Attorney at Law. When he does, all he gets is a sound much like a garbled radio transmission. Mentok asks if its encryption; Devlin states that he had a metal plate implanted into his skull after one nasty accident.
Subverted in the Halloween episode which features Bart having telepathy. Homer attempts to kill Bart but, instead of blocking Bart's abilities, Homer thinks about blocking his thoughts (and bashing his head in with a chair) but doing this before he actually does what he's thinking. Thus, broadcasting to Bart his intentions. Guaranteeing Failure Is the Only Option.
When an eavesdropping device gets turned up too high in an episode of Family Guy, everyone can suddenly hear Quagmire's embarrassing thoughts. As soon as he realizes this, he combats it by humming a John Philip Sousa march.
Quagmire's Mind: Man, this itches. I wonder who gave it to me. Probably that skank who needed a ride to the gas station. Last time I do somebody a favor... Oh God, they must have heard me! Oh God, I can hear me! Baaah ba DA da da ba ba ba da da BUM baaah da da DUM baaah da da—
Boss:You Have Failed Me. Mook: It wasn't our fault, we were outnumbered! (Boss glares) Mook:(thinking) Oh no. Must concentrate. Must not allow him to read my mind or else... Boss: So. Tell me about this one man.
Like in the Larry Niven short story "The Soft Weapon" on which it's based, in the Star Trek: The Animated Series episode "The Slaver Weapon" the crew thinks about eating vegetables to make the Kzinti telepath useless, as the thought of eating plant matter utterly disgusts the carnivorous Kzin.
In Adventure Time, Goliad attempts to read Finn's mind to reveal their plan to stop her. Finn wills himself to not reveal it by screwing with the memory of Princess Bubblegum giving the plan, doing things like turning her head into a dolphin, then making her head explode.
The titular Martin Mystery takes it a step further by not only resisting an alien's mind reading but also it's mind control by thinking about overly complicated algebra problems the entire time he is facing it.