In 8-Bit Theater, Black Mage explains that anyone who sees his face will go insane. This happens to a random passer-by which comes back to bite the Light Warriors much later. Later on, an as-of-yet unnamed Dark God tells Black Mage that hearing his true voice will cause a person's brain to eat itself.
In Ennui GO!, as Max, Cricket, Bee and the shop club brainstorm ideas on how to get revenge against Jericho for constantly breaking their creations, Bee mentions this trope by name when one of the shop kids mentions the bully shoving a baseball up someone's ass. Sure enough once they get the supplies needed, that's exactly what Max and the crew go with, as he unleashes it upon Jericho and Cyrus (and inadvertently, himself) in the appropriately named "Brown Note".
A unique tone not reproducible by nature is generated by a device that can make Florence Ambrose, a genetically modified red wolf, fall asleep or wake up. Given previous negative experience with similarly modified simians, having an "off" switch" on an experimental design is probably not all that bad idea, particularly when that "design" is a based on a predator.
Sam's real er... face, which he theorizes triggers some sort of nurturing instinct in humans, since any time someone sees it they immediately disgorge their stomach contents. This is a big part of why he wears a full-body environment suit with an animated mechanical face, beyond issues with lower partial pressure of Oxygen.
At one point, Helix creates a sculpture of Sam. A person who sees it has to be physically restrained from removing his own eyes because otherwise he "might see it again!"
The Sticky Notes of Doom, which cause any robot who reads them while connected to the commnet to download an upgrade that lobotimizes them.note They simply mention the name of said "upgrade" among the author's thoughts, and any comnet search on the name causes an immediate download and install.
The Doom Bell painfully knocks out almost all those who hear it for the first time; the print novel adaptations of the strip clarify that the sound forces the listener to directly face the fact of their eventual, inevitable mortality. Agatha, whose ancestors built the Bell, only seems mildly surprised.
Mama Gkikka: Keeds today. Kent even take a leedle existential despair.
Mama was surprised, though, that Gil found the sound "beautiful". There are many alternate theories as to why he had this reaction: it meant Agatha was still alive and fighting, he had been altered and improved by his father as a child to be more than human, and/or he's already been technically dead and revived.
In Homestuck, Feferi has to continually keep her lusus fed, or it'll cry out and every troll in the galaxy will die from the subsequent psychic shockwave known as the "VAST GLUB". Worse, since Feferi prototyped her lusus, the Black King of their session gained this ability as well, which necessitated an army of thousands of time-travelling Aradiabots to psychically suppress lest the King instantly win the battle.
In Jayden and Crusader, the character Third can apparently utter proofs of the non-existence of God so powerful Priests have heart attacks because of the conflict of their profession and the utter logic of the proof. We aren't told what this proof is.
The True Shape of Creation in Kill Six Billion Demons. The Creator themselves refuses to consider it; a goddess who tried to look at it had her eyes boiled out in their sockets, and a specially prepared Magitek expedition undergone by the Demiurge Jadis to find the Shape caused all but one member of the expedition to spontaneously disintegrate and drove the Sole Survivor — Jadis herself — irrevocably mad while ravaging her body. Even the protagonist, armed with the divine power of the creator, is forced to look away when Jadis shares a fraction of the Shape. And even the audience isn't fully immune, either; the seemingly pitch-black background of the comic? That's the Shape in a form you can understand, which slowly becomes a mysterious rainbow near the climax of the series, and you get hit with the most important part in a single strip.
Draconic, the Language of Magic in Nahast, drives people mad if they don't learn it properly.
Necessary Monsters: Jonathon tells the man on the safehouse front desk something that causes him to pull his own skull apart.
Lampooned in one series of Nodwick strips, the Evil Sorceress She Who Must Be Obeyed has obtained a written copy of That Which Man Is Not Meant to Know, and she is smart enough not to read it, because she realizes that this Trope must apply if no-one is meant to know it. However, after taking the heroes prisoner, Piffany assures her that only men are not meant to know it; women can safely read it, because it's something that they know already. When she reads it, not revealing it to the readers, the fact that such a secret would be so devastating to men almost makes her bust a gut laughing.
The Big Bad Xykon kills a room full of Paladins armed only with a super-bouncy ball. (Which has a magic symbol that cause insanity in anyone who look at it inscribed on it.)
In #859, Durkon casts Holy Word, described under Dungeons & Dragons, on the Linear Guild, banishing Sabine and striking everyone else deaf. The only member to come out unscathed is Tarquin, whose hit dice are apparently higher than Durkon's caster level. The deafness also affected Belkar, causing an interesting result when Nale cast suggestion on him to get him to stop stabbing him. Roy, who came up with the whole plan, snarks:
In Poharex, Eperok uses "The Call", a high-frequency sound(which he refers to as magic), to force any dinosaur that hears it to come and aid him in battle. He only used it once in order to distract Leay, allowing Poharex to get the upper hand.
In RPG World, it's hinted that the four Mystic Keys are these. At least it was strongly hinted that reading the Tiger Book was what made Jeff go crazy and turn evil.
For a one-shot gag in Sam & Fuzzy, here, Fuzzy creates a Brown Note video to psychologically break Sid, another character. It might have worked if Sid hadn't run away.
70-Seas has "Jensen's Ye Olde Horror of the Deep", an Eldritch Abomination in a bottle that causes pants-wetting terror on anyone looking at it.
In "The Terrible, Horrible, No Good, Very Bad Day" arc of Skin Horse Nick was assigned to compile a sound-based weapon against biologicals. It knocks out the entire building, though the staff of Project Skin Horse, being either robots, undead, canine, or a former werewolf, recover before the rest. At one point Tip calls it a Brown Note.
The sculpture known as "The Spine of the Cosmos". Looking at it by itself is harmless, but when its artistic context note which involves Yeats' poem The Second Coming is described to the viewer, they are either granted ultimate understanding of the universe or driven insane — either way, becoming a mindless zombie. The insectoid aliens known as Cirbozoids are the only intelligent species immune to this, due to their inability to understand art. It is forever robbed of this ability, however, when its artistic context is irreparably changed by Mr. Jinx wearing it as a hat, and is thereafter described by at least one character as "the dumbest thing i've ever seen
The Troll King's Seven Deadly Words in Tails Gets Trolled, when said, shut down a part of the listener's body.
Ubersoft employees were once shown only the shadow of a new Apple product, since its beauty drove a small percentage of the population insane when they looked directly at it. When asking how big a percentage, the answer was approximately the same small percentage of the population that had been allowed to look at it directly.
Librarian Dewey develops a book talk guaranteed to make people faint in Unshelved! He also has, if memory serves, book talks that make people nauseous, break out in a rash, and speak Urdu, among what must be others.
Vexxarr has the Schlumpoid Sploorfix, whose Livejournal entries have caused AI to explode at how melancholy they are. Even his casual observations about life have caused otherwise rigidly-programmed ship drones to consider him a threat to the host vessel and left him unceremoniously dumped in a waste bin.
Now, if you see a puddle in the street, SWERVE TO AVOID IT. I know you think that would be more dangerous, but these tires are so worn-down that their molecular structure has degraded to an as-yet-undiscovered chemical compound that explodes on contact with water. The radio is pretty safe to listen to, but don't switch it to AM frequency. The ear-piercing squeals that are emitted will haunt your dreams and drive you to insanity.
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