Mustrum Ridcully is a fan of Wow-Wow Sauce. Its ingredients include scumble, sulfur and saltpetre (two of the primary ingredients in gunpowder), and grated wahooni (a particularly pungent root vegetable). It's also occasionally used as a weapon. An illustration in Nanny Ogg's Cookbook shows Ridcully preparing it wearing metal gauntlets, a padded leather apron and a welding mask, with the sauce bottle behind a cast-iron shield. After a large meal that included a large amount of the sauce, Ridcully's uncle had a charcoal biscuit (the third primary ingredient in gunpowder) to settle his stomach, lit an after-dinner cigar, and "vanished in mysterious circumstances". They found his shoes on the roof the next spring.
In Hogfather a presumably different uncle used to swear by Wow-Wow Sauce (or at it, or possibly both) as a hangover cure. After drinking a whole bottle in one go, "he seemed very peaceful when we came to lay him out." Ridcully also mentions in this book that Wow-Wow Sauce isn't safe to drink while the sweat's still condensing on the bottle (not unlike nitroglycerin).
In Unseen Academicals, Pepe knocks back an entire bottle of Wow-Wow while rooting around the Night Kitchen of Unseen University in the background of a scene. He notes, in a strangled tone of voice, that it would probably be good with vodka; the narration points out that by all rights he should no longer have a stomach.
The Compleat Discworld Atlas mentions the Vanglemesht Red Python Chilli. A single pepper could flavour five hundred pots of beans, as long as everyone liked them spicy. It is, of course, an ingredient in Wow-Wow Sauce.
A throwaway passage in Neal Stephenson's The Diamond Age mentions a bottle of sandwich sauce containing "imported habanero peppers", "butts of clove cigarettes", "uranium mill tailings", "nitrates, nitrites, nitrotes and nitrutes, nutrites, natrotes..." and a Long List of similar items.
Hotroot pepper in the Redwall books. Best guess is that "hotroot" is the local term for a type of horseradish. The otters love the stuff, especially in "shrimp'n'hotroot soup", and hold contests to see how much they can use at once.
In The Areas of My Expertise, John Hodgman notes that he tried to write a review of these sort of sauces, but after he tried eating one on the low end on the scale on a small cracker, he had to lie down on the couch and cry for the rest of the day. The column was rejected for being "overly gay."
Some of the "ultrahot hot sauces" described promise not only your death, but the obliteration of the entire universe.
Jon A Jackson's Fang Mulheisen series of police novels feature a Mafia gangster named Umberto who is addicted to extremely strong Latin American chilli sauces.
At one point in The Malloreon, during a state banquet, the heroes try a seemingly-inoffensive rice dish. Turns out it's from their world's answer to India, populated primarily by elephant herders who even treat mealtime as tests of personal courage, and "spend the rainy season trying to build bonfires in each other's stomachs". As most of the cast lunge for the water decanter, Sadi calmly keeps eating the stuff. He's not affected because he's used to being poisoned.
In The Bloody Road to Death by Sven Hassel an Ethiopian boasts of being able to eat anything put in front of them. Cue the Italians putting 'Red Devil Sauce Number One' on his food. Hilarity Ensues.
Secret City's Navish Shurk' consists of three sorts of meat, finely chopped note "(to) chop (someone)to Navish Shurk'" is a local proverb referring to gratitous violence , fried, then boiled in one such sauce. To top it all, it's served on a double-decker dish, the top contains the meal itself and the bottom is filled with burning alcohol to keep it boiling while you eat it. However, it's also so delicious that, when a policeman not aware (yet) of The Masquerade accidentally ordered and tasted it, he immediately ordered more for himself and his wife. As he told his superior next day while drinking sixth bottle of water, it was Worth It.
The South Amareican chili pepper in Rainbow Dash and the Daring Do Double Dare. A couple of them would be a valid pest control method for farmers, and one bite caused Rainbow Dash to hallucinate and spew rainbow-colored fire.
In Janet Kagan's Star Trek Expanded Universe novel Uhura's Song, the catlike Sivaoans use the berry of a native bush as a spice. They call it a "tail-kinker" and a favorite prank is to slip a few of the fresh berries into a dish rather than the processed version. Think getting something you think contains a bit of red chili flakes but instead has whole Sichuan peppers in it.
Played for Laughs in Volume One of The First Dwarf King. Jani takes Eustathios to a mead hall called Blazing Beers.note No, the title is NOT a pun based on this trope; it's purely coincidental — the name comes from the huge bonfire in the middle of the hall, which continually belches off blinding smoke. The owner finds out that Eustathios is an elf. He then puts hot pepper in Eustathios' drink, and instructs Jani to give it to him without letting him know what's in it, which Jani does. Unfortunately for the dwarves, Eustathios likes it.
Chakona Space features the Tales of the Folly series. The Folly's rabbit chef likes to add this kind of spice to meals when she thinks her captain or fellow crewmwmbers aren't paying attention to her culinary efforts. She has learned to tighten up her aim after a group she wasn't targeting ate the spiced up food she left out for the captain, who skipped a meal.
She put four drops of a rare, Caitian spice into a half-full pot of stew when a single drop would have been sufficient for a full pot.
This is what happens when Able Team try eating the food in Sri Lanka. It's even worse that night when the food comes out again, described by one team member as 'napalm shits'. Ironically that saves their lives, as a hit team tries to kill them when they're asleep in their beds, only to find all three awake and annoyed on the toilet.
Chef Chow's Hot and Spicy Oil in Daniel Pinkwater's Borgel. It is described as being dangerously explosive, and at one point is used to kill a giant.