Mustrum Ridcully is a fan of Wow-Wow Sauce. It contains scumble, the essence of a number of particularly pungent apples, and two of the primary ingredients in gunpowder, and is 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 lit an after-dinner cigar and vanished in mysterious circumstances. Well, not that mysterious: Wow-Wow sauce includes sulfur and saltpeter (2/3 of the recipe for gunpowder), and he had a charcoal biscuit before the cigar (the remaining 1/3). They found his shoes on the roof the next spring.
As mentioned in Hogfather, a presumably different uncle used to swear at it (no, not by it, at it) as a hangover cure. After drinking a whole bottle in one go, "he seemed very peaceful when we came to lay him out."
The curry Susan tastes in Soul Music causes the air to explode after she throws it away.
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.
According to the book that introduced it, Wow-Wow sauce isn't even safe to expose to air until the bottle has stopped sweating, and the scumble that makes up its base? It's an alcoholic beverage that no one has ever accused a bartender of watering down, due to what happens when water touches it.
That "sweating" is a reference to nitroglycerine for crying out loud.
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 Mallorean, during a state banquet, the heroes try a seemingly-inoffensive rice dish. Turns out it's from their world's answer to India. As most of the cast lunge for the water decanter, Sadi calmly keeps eating it. He's not affected because he's used to being poisoned.