Some people cannot cook. They burn breakfast so bad that you lose your lunch preemptively. When they cook dinner, you can only think of dessert-ing. Sometimes, if you're lucky, they can cook something that can be charitably described as "food."
Sometimes their food merely tastes bad. However, it has also been known to cause nausea, vomiting or hospitalization. If you're particularly unlucky, it can cause, well, just about anything. If dinner eats you, you're probably in a lethal chef's kitchen.
As you may have guessed, this is usually a comedy trope. In eastern media, most examples are female, but there are a ton of male examples in western media, probably tying in to the assumption that Men Can't Keep House.
There are a number of common variants. Sometimes someone is forced to stomach the lethal chef's food to avoid hurting their feelings. Sometimes they refuse to admit that they can't cook, despite mountains of evidence. And sometimes, if you're particularly lucky, their food merely looks bad, and tastes perfectly fine.
Lethal Chefs may be employees of a Lethal Eatery, and quite often can be found fixing up a stew of Mystery Meat.
Compare the Cordon Bleugh Chef who can cook just fine, but often gets too creative, the One Note Cook who can ace one dish, but otherwise falls into this trope, and the Evil Chef who just likes to see you suffer. See also Lethally Stupid when the character is so dumb it would be dangerous to let him cook. Contrast the Supreme Chef, who is the exact opposite of this trope, and the Chef of Iron, who can be either bad or good but is lethal outside of their cooking.
In a commercial for Pokemon cereal, a mom attempts to cook her kids breakfast based on Pokemon characters. Unfortunately, in the process of doing so, she ended up burning the food.
ThisHomestuck fanfic describes Dave as one, to the point where his sylladex refuses to acknowledge his creation as "spaghetti", or "pasta", or even "food". It takes him and John only a few bites to decide it was right.
Derpy Hooves isn't much better in Were Gonna Get There Soon. Played for Drama when she's tasked with bringing snacks for the next Weather Team meeting, and she promises herself she'll prove to them that she's able to complete a task without it ending in disaster. She's on the verge of tears after several attempts result in flaming muffins, muffins that are simultaneously undercooked and overcooked, and turning the kitchen into a disaster area that gave Thunderlane's mother an aneurysm.
The Worst Bakers In Equestria is about a lethal chef competition started by someone who earned her cutie mark in bad baking. The cooks are so bad that they make biscuits that explode, somehow attract a bear, manage to swap a major ingredient with a sauce made of near-pure rainbow extract, which probably wasn't in the ingredients to begin with, put a taster in a coma for a year, have eggs somehow turn out to have live chicks in them, make food that went straight back around to being utterly perfect, and the reigning champion, Rainbow Dash, somehow managed to create blueberry muffins, while trying to make cookies. Supervised. Nothing went wrong during baking process, and blueberries were not an ingredient.
In The Emiya Clan, Kiritsugu Jr manages not only to make food that you can't eat, but also to make food that eats you. Whatever he cooks somehow comes to life as some kind of Eldritch Abomination. This includes (but isn't limited to): Sliced cucumbers becoming tentacle beasts, boiled water becoming flaming water spirits, roasted chicken turning into an undead monstrosity that is almost impossible to kill, and fried bacon becoming sentient, escaping into the basement, building an underground civilization based on the worship of his daughter, and vowing vengeance on the surface world.
His sister Chiyo also cooks notoriously badly, but while her food might taste so bad it almost kills you, it's so healthy you feel like a million bucks afterwards.
Vili in The Tainted Grimoire put poison in the meal she cooked for Luso, Crow, Hurdy, Kanin and Adelle when she mistakenly thought it was just seasoning.
In the Fanfiction story Percy Jackson Olympus Divided, Thalia Grace is said to be this, with comments suggesting her oatmeal was bad enough to put Artemis, a goddess, in the hospital. When she ate her own pancakes...she ended up in the hospital.
In the former series Naruto Alternate Dimension, Tayuya is described to be this, ending up turning a cheesecake into something from an alien movie that had to be buried in cement, her attempts at muffins ended up breaking holes through solid stone and randomly set things on fire just trying to make cereal. Tenten is also described to be a bad cook, blowing up a microwave at least once.
In More Than Human, Blossom is such a disaster waiting to happen around cooking that Buttercup declares that there is a 15-foot perimeter around the grill that is a "No Blossom" zone. One ruined batch of hamburgers later, Blossom reluctantly complies with her sister's mandate.
Rainbow Dash is revealed to be one in Magnetism, managing, like Sweetie Belle in the My Little Pony: Friendship Is Magic example, to liquify burnt toast. Fluttershy almost eats it to make her friend feel better, but Angel tosses it out the nearest window.
In Ronin-ai'sFinal Fantasy VIII universe, Irvine Kinneas is this, so much so that Squall Leonheart learned to be a very good cook in "self-defense".
Lind in Ah Archfall has terrible cooking skills, possibly linked to her lack of magic.
In The Non-Bronyverse, TD is a terrible chef, whose skills are on a par with Sweetie Belle's, as Rarity is unfortunate enough to experience first hand.
Legendary Genesis has Chef Muk, who's supposedly an exceptional cook in spite of her unsanitary habits. According to Dion, everybody at Arcanine's Academy has developed an immunity to her cooking.
Suki in The Stalking Zuko Series has food that tastes like congealed sadness and burned a roast to an inedible crisp. Sokka ate it anyways because he loves her. Justified in that she never had to cook before as the other Kyoshi Warriors did. She gets better in Not Stalking Firelord Zuko when she makes a dish that's tasteless but edible. She's learning.
An ancient Chinese story tells of a comatose general being saved from hunger by two beggars. The dish in itself was terrible (consisting of trampled spinach, rotten beancurd and unpotable water), but he didn't notice because he was semi-conscious, instead thinking it delicious. When he became emperor, he ordered said beggars to present said meal to his ministers. Afraid to lose face, they all gulped it down. The Emperor, realizing how horrible the dish was, still drank it all. The two beggars ended up rich.
Films — Animation
In Ratatouille, Linguini, before meeting Remy, makes a soup so bad that when he tastes it he pukes and Remy nearly does too when he sniffs it. Yes. His food is so bad that not even the rats will eat it.
The standard food in the colony in Titan A.E.: "I'd just like them to kill my food before they serve it to me. I do an honest day's work, I want already-dead food."
Roger Murtaugh's wife from the Lethal Weapon series is not known to be skilled in the kitchen, as evidenced by the following exchange:
Murtaugh: What the hell, thin's my middle name.
Riggs: Your wife's cooking, I'm not surprised.
[fires his gun several more times]
Murtaugh: What? What?
Murtaugh: Remarks like that will not get you invited to Christmas dinner.
Riggs: My luck's changing for the better every day.
Lane Meyer's mother Jenny (played by Kim Darby) from the 1985 John Cusack film Better Off Dead. In one scene Jenny is shown cooking a pot full of something emitting a suspicious mist from which tentacles wave, and in another, one of her dishes actually crawls off of Lane's plate when he pokes it with a fork. Even her "ordinary" meals are somewhat ... skewed, as evidenced by the "French-themed" dinner she makes for a French exchange student — consisting entirely of foods with the word "French" in their names, like French dressing and French toast.
"It's got raisins in it... you like raisins!"
The extended edition of The Two Towers reveals Éowyn to be a terrible cook, who proudly presents Aragorn with a bowl of "soup" containing some limp boiled leaves, one gelatinous dumpling, and a puddle of liquid shimmering with grease. As a royal princess who seems to disdain feminine activities, it makes some sense that her cooking skills are underdeveloped.
Jack Black's character Nacho from Nacho Libre is like this initially. Once he makes enough money (through his wrestling) to purchase better ingredients, he's capable of making dishes that at least look appetizing.
In the first Bridget Jones book (and movie), Bridget attempts to cook soup from scratch. The recipe says to tie some of the ingredients together with string before putting them in the pot. She uses blue plastic string and turns the soup blue. It's later referred to as String Soup.
Isabelle in The Dreamers cooks for narrator Matthew and her brother Theo. The food is so badly burned that they can't tell the souffle from the ratatouille, and tastes so bad that Matthew can't swallow it. Theo happily goes downstairs and raids the neighbors' garbage for an alternative meal.
In Jack Frost (1997) the Sheriff manages to find out the killer snowman is vulnerable to antifreeze after it is exposed to his son's brownies. His son apparently put highly-toxic antifreeze in these brownies because he did not want his father to get cold.
Bullshot. Rosemary Fenton's rock-hard scones are an ongoing joke. When the hero nearly breaks a tooth on one and tries to covertly dispose of the scone, he finds every hiding place in the house already stuffed with scones discarded by previous guests.
Miller:(seeing their dinner) You son of a bitch, Humphrey. Humphrey: Come on, you haven't even tried it. Miller:(Miller takes a mouthful) You son of a bitch, Humphrey.
In Down Periscope, on the submarine Stingray, hyper executive officer Marty Pascal (played masterfully by Rob Schneider) is berating the cook, Buckman, for the ill-kept nature of his kitchen, when he spies an open can.
Pascal: Jesus, Buckman! This stuff's been on the Stingray since Korea! This can expired in 1966!! Buckman:(tastes from the can) What's the matter, sir? It still tastes like creamed corn... Pascal: Except it's deviled ham!! Buckman: ... That would be a problem.
The classic Laurel and Hardy short "Saps at Sea" has them cooking breakfast for a thug. But there's no food. So they make a fake, substituting brewed chewing tobacco for coffee, string for spaghetti, red paint for sauce, sponges for meatballs, grated soap for cheese... Unfortunately he finds out and tells them to eat it first.
In the first Charlie's Angels film, Lucy Liu's character Alex makes completely inedible muffins. Another Angel throws one at a door, and it almost goes through, getting stuck in it.
The lunch cook in Principal Takes A Holiday is shown to make barely-edible food. When the new fake principal decides to try it, he goes to the kitchen in disgust and forces the cook to eat his own food, telling him he'll have to do this from now on. When the real principal shows up, he remarks how things have improved, including the fact that the food is actually pretty decent now.
In the film version of The A-Team, Murdock shows some shades of this. His preparation of steak involves sprinkling cordite on them, and then flipping them over to allow it to flame up. His "special sauce" (containing anti-freeze), induced Bell's Palsy in Face (which Murdock shrugged of as "only partial paralysis"). What keeps him from being considered a full-on lethal chef is that he has been shown to be really good at the job as well. His curry tapenade is what is used to calm down B.A. after his being drugged and brought on board a ship.
In the Danish Pusher film series, Serbian druglord Milo runs a restaurant as his cover and likes to feed his criminal associates his creations, which are apparently terrible. In the third film, he gives his whole gang food poisoning right when he needs them most, leaving him to his own devices.
Spike Jones' "Pass the Biscuits, Mirandy" is told by a Tennessee mountaineer whose wife is one. At least when it comes to her biscuits.
"Could kill a man twice after eating a slice of Miss Fogarty's Christmas cake."
The mess sergeant from Tom Lehrer's "It Makes a Fellow Proud to Be a Soldier":
Our old mess sergeant's taste buds had been shot off in the war
But his savory collations add to our espirit de corps
To thing of all the marvelous ways
They're using plastics nowadays
It makes a fellow proud to be a soldier.
Another Tom Lehrer song where this trope made an appearance was "She's My Girl."
So though for breakfast she makes coffee that tastes like shampoo, I come home for dinner and get peanut butter stew, Or if I'm in luck, It's broiled hockey puck, But, oh well, what the hell, She's my girl, And I love her.
I Love Bees: Kamal is a male example. He microwaves a whole raw chicken, cuts it up in exactly equal slices, and in place of Worcestershire sauce and butter uses ketchup and butter-flavored popcorn oil.
The Swedish Chef of The Muppet Show is generally a unique example of this (i.e. his cuisine is lethal to him), but he occasionally plays it straight- in one instance he went into cordon bleugh territory and made an onion cake; in another, he provided a quite literal example.
In The Navy Lark Able Seaman "Fatso" Johnson's pies prove to be rather convincing as limpet mines, and less edible.
Grytpype-Thynne: (sipping soup) Tell me, Moriarty...what is this foul but economical recipe? Moriarty: It's a family secret! Grytpype-Thynne: Why? Moriarty: They died after the first mouthful. It was terrible! I had to do all the washing up myself!
In Cabin Pressure, Arthur consistently fails to cook edible food. At one point, he spectacularly fails at reheating frozen food. Unfortunately for everyone, he's usually the cook.
In Entropy Inc's Star Wars campaign, the title crew stole/refurbished a cooking droid. Unfortunately, everything it made tasted like bantha burger.
In Sweeney Todd: The Demon Barber of Fleet Street, we first meet Mrs. Lovett while she's telling Sweeney (and us) how awful her meat pies are ("The Worst Pies in London"). The song "God, That's Good!" subverts this trope, as it suggests that Mrs. Lovett is actually a pretty good cook, she just needs to buy high-quality ingredients ( such as with the money taken from Pirelli's corpse).
The entire plot of Nunsense is set into motion in the aftermath of Sister Julia, Child of God, having killed all but five of the Little Sisters of Hoboken with a tainted batch of vichyssoise soup.
Presumably out of amusement, Riko in A Profile occasionally makes completely inedible lunches for Masayuki. She's a perfectly competent cook, she just does it for fun.
The anime actually managed to combine Sanae's bread with Ayu's special jam listed below. The result was truly something to behold.
Ayu in Kanon was a terrible baker early on. She's quickly instructed in decent baking by Akiko in the absence of any real Supreme Chef, Yamato Nadeshiko etc character. That being said, before she improved, Ayu managed to burn rice and turn eggs into what seem to be solid lumps of charcoal. The cookies were so inedible that he couldn't even eat them to be polite as his teeth couldn't break them! Her special jam, however, is never edible.
Hisui from Tsukihime cooks so badly it's considered poison if anyone but her eats it. For various reasons, no one but Ciel is willing to tell her how bad she is.
Sengoku Rance gives you Kouhime, whose dango is actually praised by a ninja... as a great assassination tool. And she made said dango under the guidance of the ninja, who is a Supreme Chef.
While she can make rice just fine, anything else Minori from Brass Restoration tries to cook falls squarely in the lethal category.
Both Jason and Melissa in the beginning of the visual novel Songs of Araiah. In Melissa's case, she's been eating her own horrible cooking for so long that she enjoys Jason's cooking, which would be lethal cooking by anybody else's standards. Both improve their skills to a degree by the end of the game.
Yukino from My Girlfriend is the President, to the point where when she tries to make a bento for the player character, it's covered in censor mosaics.
Yuuka in Never7. Her attempt to make toast ends up producing a horribly burnt mess with an even more horrible spread.
Elis in Canvas 2 is apparently completely unaware that she's a horrible cook.
Uruka and Aselia in Eien no Aselia have a little too much confidence for people who have never cooked before. Aselia at least makes an effort to start learning to cook properly after this.
Akira is said to often have "blow(n herself) up" while cooking, with her blind younger sister Lilly doing a better job.
Shizune Hakamichi doesn't even seem to understand the theory behind the food she cooks. Could be explained by the fact that she's filthy rich and may not have had to ever do much cooking herself, not to mention she tends to order take-out food more than once.