Pokémon: the Spelon Berry; description: "So spicy is the Spelon Berry that, Fire type or not, Pokémon will try to breathe fire after eating a single one."
Whatever Mallow had the player whip up in Pokémon Sun and Moon, neither Lana nor Kiawe could handle a single bite of it.
The Jalapeño in Plants vs. Zombies can instantly burn all the zombies in a single lane. The sequel introduces the Pepper-pult, which deals fire splash damage and also warms up plants around it, and the Wasabi Whip, which deals heavy close-range fire damage and also warms plants.
In Tales of Monkey Island, there is the fugu jolokia, a chili pepper so hot, you can't touch it with your bare hands without getting burnt. You have to hold it to your tongue for eleven seconds.
World of Warcraft has (sadly outdated) Dragon Chili, made from mystery meat and a small flame sac taken from baby dragon bodies. Every so often after eating it, the character will breathe a damaging cone of fire on anything they're fighting.
The Jabañero pepper in Kingdom of Loathing is evidently so spicy that "Just thinking about it makes your mouth hurt." Putting one in a spicy enchanted bean burrito, then eating one, gives one the (fairly useful) skill 'Chronic Indigestion'.
Some servers in Space Station 13 let you create ghostlier chilis, a chili pepper hot enough to make whoever's foolish enough to eat one burst into flames. If the botanist making one gets it just right, it can turn people to ash in a single bite.