Scrooge's chili, in "Ducks of the West". It turns everybody who eats it (aside from Scrooge) into a Fire-Breathing Diner. Scrooge's unintentional victims then head to a nearby horse trough to cool out their mouths.
Scrooge: I may be a city slicker, but we'll have a hot time in the old town tonight!
Ma Beagle's homemade chili in "The Masked Mallard". The Beagles use it to melt glass and (attempt) to steal a diamond.
Big Time Beagle: Ma's homemade chili. The most corrosive substance known to man.
The Diablo Sauce in Kim Possible, which Ron uses packets of for hand warmers at one point. They're spicy enough to fry a robot's circuits.
The Merciless Hot Pepper of Quetzalsacatenango, also known as the Guatemalan Insanity Pepper from The Simpsons. They're "grown deep in the jungle primeval by the inmates of a Guatemalan insane asylum." Homer has to lacquer his mouth and esophagus in order to eat one, and is still driven temporarily insane by its spiciness.
Hermes from Futurama, in the episode "The Six Million Dollar Mon", spilled a drop of sauce from his wife's spicy curried goat, and it ate its way through the dining-room table, the floor, two other residences underneath, and on down to Robot Hell, where it scalded the Robot Devil. Hermes himself thought it needed more hot sauce.
Fortunately, this ends up saving him later on in the episode; years of his wife's overly spicy cooking somehow made his skin extremely spicy, and when Ax-Crazy robot Roberto eats a piece... he melts.
Beavis and Butt-Head: The Missing Episode "Down Mexico Way" has our Anti Heroes decide to try the local cuisine. While waiting, they torment a dog by force-feeding it the bottle of "Killer Hot Sauce" on their table. This pisses off the Mexican cook, who reaches for the "Mexican Death Sauce" (which is in a bottle with smoke coming out of it) and puts it on their tacos. Cue Fire-Breathing Diner. (This scene even provides the page image for that trope.)
On SpongeBob SquarePants, Sandy threatens SpongeBob with a single drop of hot sauce to the tongue. A drop of hot sauce that talks.
"By the powers of naughtiness, I command this particular drop of hot sauce to be really, reallyhot!"
After SpongeBob surrenders, she casually starts gulping the stuff down like it was lemonade.
A staple for food-related pranks in Looney Tunes cartoons; often the effect can be done with plain old tabasco sauce.
As very spicy mustard (which features a different chemical than capsaicin to produce its spice) used to be much more common, some older works feature this instead of the modern hot sauce. Tom and Jerry features this in several episodes.
You can get very hot mustard as a condiment at your average Chinese take-out restaurant. WARNING: Do NOT eat more than a light glaze of this stuff on your food - unless you have a cold and you really want to clear out your sinuses.
Very hot mustard is also commonly found in Russian cuisine. In Russia, you can buy this stuff in quite large jars cheaply.
In My Little Pony: Friendship Is Magic, Pinkie Pie apparently loves this. She likes to put it on cupcakes. Her brand is so hot that, when Twilight Sparkle accidentally drank some, her tail and mane caught on fire and she let out the classic "train whistle" steam clouds out her ears.
However, not even Pinkie can handle the spiciness of liquid rainbow* yes, literal rainbow. She turns different colors and breathes a small gout of flame before going weak on her knees and running off, presumably to get something to abate the taste. Keep in mind that this is a character that eats pastries with hot sauce. However, nowhere in the series is liquid rainbow used as a spice.
In the Hey Arnold! episode "On The Lam", Harold, Stinky, and Sid launch a rocket filled with vinegar, baking soda, and Stinky's bottle of Louisiana Hot Sauce, which they believed to blow up an old police station with, when it was really demolished by Ernie.
The "Honor Thy Ed" episode of Ed, Edd 'n' Eddy starts with the Eds having set up a taco stand selling "tacos" made of paper plates, grass, and shredded crayons. After Ed, Extreme Omnivore he is, eats several crayons thinking they are flavors, Edd humors him and takes a bite of one. He is disgusted and needs water, but the closest thing is Eddy's Brother's Armenian Secret Hot Sauce. He guzzles part of it and seems unfazed at first. Ed also consumes some. Eddy thinks the sauce didn't work and also eats some. It's at that moment the effect takes hold, however. We see a Discretion Shot from down the street as a tower of flame erupts from the stand and the Eds sticking their mouths on a sprinkler.
"Grandpappy's Texas Tin-Horn Sizzlin' Salsa Sauce" in Xiaolin Showdown. Two bottles of it turn Dojo, a dragon who can normally only breath soot clouds, into a volcano.
Chowder gets a whole episode based around this, considering it's a cartoon about food. The episode (aptly named "the Fire Breather") introduces the rarest and hottest peppers in the world, the Dancing Diablos. Peppers so hot that it turns your stomach into a furnace and makes you breath fire every time you open your mouth. Guess who decides to eat all of them?
Garfield had Grandma's sausage gravy in A Garfield Christmas. It started out as Mom's normal gravy, but Grandma snuck in and added chili powder while whispering about how her gravy won first prize at the fair three years in a row while Mom's didn't even place. A bit later, Garfield comes in and gets some on his finger, then licks it. Cue the fire breath a second later, and then Garfield going "Perfect!".
Regular Show: When Mordecai and Rigby try to pass off an unconscious Benson as awake, they get him involved in a spicy food contest with a guy. Benson comes to just as the guy prepares a concoction he calls "Mississippi Queen", so he has Mordecai and Rigby drink it as well. At first they feel nothing, but suddenly start hallucinating and wake up the next morning in the park.
Taz-Mania: In "Francis Takes a Stand", Francis switches Taz's lemonade recipe with a recipe for a Blazing Inferno Hellfire Sauce. Naturally, Francis ends up drinking more of the stuff than Taz does.
Grossology: Pink-Eye attempts to torture Lance Boil by force feeding 10 bottles of this stuff. It fails because Boil has replaced his stomach with an artificial digestive system.
Storm Hawks gives us Skyside Shanty's signature extra potent, quadruple malt vinegar.
Junko: Kinda sour, but I like it.
Finn: What a shock.
The super-hot chili peppers that prove to to be the best defence against the mutant raccoons in the Camp Lakebottom episode "High Plains Garbage Eater".
In The Smurfs episode "Gingerbread Smurfs", Brainy has Clumsy add volcanic lava juice to his recipe for making gingerbread cookies to make them really spicy. It is so powerful that it blows up the kitchen when it is added.
In one episode of Batman: The Animated Series, a goofy villain calling himself the "Condiment King" dealt with someone who tried to stop him by squirting him in the mouth with a packet of hot sauce.
In the "Too Young" episode of Adventure Time, Princess Bubblegum accidentally invents a Blazing Inferno Hellfire Sauce while trying to create a new bath product.
In the Mixels Moon Madness special, Rokit's hot sauce causes a Nixel to go up in a mushroom cloud when Rokit offers the sauce to him, then it comes back down after a few seconds. When Rokit eats the sauce, his head flies off.
One episode of Adventures of Sonic the Hedgehog had Scratch and Grounder attempt to capture the blue blur by setting up a fake chili dog stand. Sonic disguises himself as a "chili dog inspector" and critiques Grounder's chili for not being spicy enough. He "helps" Grounder by giving him a can of "Very Hot Chili" to add to the mix and then tricks Grounder into eating a hot dog covered with said chili, causing the latter to explode like a rocket. Sonic then proceeds to serve two dogs (with regular chili) for himself and Tails.