Lunch Lady Doris routinely serves truly abominable food to the students at Springfield Elementary. It's implied that her incredibly poor cooking is caused atleast in part by the ridiculously low budget Springfield Elementary recieves from the state, but part of it is her own apathy and incompetence. Some examples of her culinary failures:
From season four's "I Love Lisa," Lunch Lady Doris serves beef hearts to the kids (it's Valentine's Day)... after the delivery guy reluctantly dumps them on the dirty floor. If you listen closely, one of them is still beating.
In a season 5 episode, she's shown preparing a meal that consists entirely of testicles. Why? More testicles means more iron. In a disturbing turn, she's surprisingly animated about that one.
From season seven's "Lisa the Vegetarian," it's revealed that Lunch Lady Doris doesn't cater to vegetarians (except for giving them a plain bun and deadpanning, "Yum. It's rich in bunly goodness.") and that the meatloaf she makes isn't made of meat.
She has also been known to use shredded newspapers and gym mats. Skinner justifies the former by saying they add "roughage and essential inks". Doris' only complain is that there is very little meat in the gym mats.
One episode has Lisa find a battery in her Mac N Cheese. Doris claims it "counts as a vegetable".
Homer himself cannot cook, feeding into his general ineptitude:
On the season four episode "Marge in Chains" (where Marge is put in jail for 30 days after accidentally shoplifting bourbon due to being stressed out from her family being sick), Marge flashbacked to the last time Homer tried to cook for the family. He served fish that weren't quite dead—and the lobsters attacked him. On the same episode, he gave Bart pack of sugar and some peanut butter smeared on a playing card as a school lunch.
During Marge's stint as a professional gambler/gambling addict in the episode "$pringfield", groceries run low at the Simpsons house, and Homer attempts to make "breakfast" by mixing together cloves, Tom Collins mix and a pie crust. He takes one bite, before telling Lisa they're going to go get Marge back in a disturbingly calm voice.
Marge herself is implied to be kind of an uninspired chef ("Eight spices? Some of those have to be doubles! 'Ore-gahno'? What the hell?"), but as her family just shovels it down anyways, there are no complaints. There's also a mention of her making Bart butterscotch chicken (which, oddly enough, people have actually made) on the season eight episode "A Milhouse Divided." Which is odd, since Bart had previously been established as being allergic to butterscotch...
Mr. Burns seems to be rather bad at it, judging by the expression on Smithers' face when he tastes a cake that Burns baked in the episode "Scenes from the Class Struggle in Springfield". "I pickled the figs myself."
The Springfield prison chefs are known to be horrible, even by prison standards. In the episode "The Seven-Beer Snitch", the prisoners were fed "horse meat... with traces of jockey meat". Cue camera to a box of "Churchill Downs Mystery Meat".
Nelson's mom once sent her son to school with a drywall sandwich for lunch.
Futurama: Bender, being a robot, has no sense of taste and a limited knowledge of organic biology. As a result, he has trouble understanding why humans dislike food that only contains 90% of a lethal dose of table salt. He even ended up accidentally killing his Obi-Wan Kenobi-esque culinary teacher with a dish that made his stomach implode, though his mentor at least declared it "acceptable" before dying. He also once made drinks that melted through the floor when spilled. The episode "A Leela of Her Own" also featured aliens called Cygnoids, whose bizarre physiology and foreign culture led to many problems, including "wine" made from crushed rats. (However, their pizza crust made with wasps seems to be a real hit). However, in "I Second that Emotion" Bender bakes an amazing cake. So it seems that he can make good food if he follows the recipe to the letter, but he has a tendency to experiment, so...
Leela: Oh, dear God! Fry: That's the saltiest thing I ever tasted, and one time I ate a heaping bowl of salt! Amy: Bender, is this salt water? Bender:It's salt with water in it, if that's what you mean. Fry: My vision's fading... I think I'm gonna die! Bender: There was nothing wrong with that food. The salt level was only ninety percent of a lethal dose. Zoidberg: Uh-oh. I shouldn't have had seconds.
Granma Stuffems is a very extreme example. The food is literally alive and acts as her helpers, forcefully stuffing themselves into kids' mouths. And also that giant sandwich creature Slamwitch is one meal that could probably make a meal out of you.
Lizzie, #1's girlfriend, is also pretty bad. When "Nigie" is sick, she makes him soup that he later uses as an explosive weapon. When he goes on a retreat in Jamaica, she follows with a pie she baked for him. One bite of the pie knocks the pilot unconscious. And then the replacement pilot.
There are often jokes about the lethality of cafeteria food at The Skool, including missing livers if the kids are lucky. One of the more noteable dishes is Ketchup and Rice. Another is some unknown sludge-like substance stored in a tank in the Skool Cafeteria ceiling that crawls inside the students eye sockets after being served.
"GIR, your waffles have sickened me! Fetch me the bucket!"
Grandpa Max from Ben 10, mostly because being one of the plumbers exposed him to some very odd cuisine. While his cooking may not strictly be lethal, it's generally... rather strange and somewhat unappetizing, the first example being a wriggling bowl of marinated mealworms. This is a Running Gag for the series. At one point, Max pulls a grubworm out from under a log at Yellowstone and eats it, much to the disgust of his grandchildren. Naturally, alien plumber Rook considers him a Supreme Chef.
X-Men: Evolution's Kitty Pryde is an example of this early on (her muffins either bounce off the walls or leave dents in the floor; poor Kurt), but gets a little better with constant practice as the series progresses.
Jon Arbuckle, in Garfield and Friends, is frequently portrayed as a Lethal Chef; his "new recipes" invariably end up as something that looks like it belongs in a low budget horror movie, although he is also usually capable of making normal food when he's not trying to get creative. However, sometimes he even fails at that. In one episode, Jon attempts to cook breakfast. With the Rule of Three fully in effect, the first two food items he makes, which require actual contact with flame, catch fire. Jon then gives up and decides to have some cereal. When he pours milk on his cereal, it promptly catches fire. Jon's specialty, deep fried pigs liver with chocolate sauce, is so revolting even GARFIELD wont eat it. In one episode, he prefers eating the pictures out of a cookbook.
Squidward seems to be something of a gourmet (albeit one with an affinity for canned bread and marzipan), and, in at least one episode, is seen eating what has all indication of an elaborate and tasty dish prepared by himself. However, when asked to sub as cook at the Krusty Krab, all he manages to do is burn everything to a crisp, suggesting he's at least a lethal fry-chef.
Likewise, the main reason Plankton is always trying to steal the Krabby Patty formula is because his own cooking is highly unappetizing. One episode had Karen (Plankton's computer wife) paying a guy to eat at the Chum Bucket (Plankton's restaurant). He gave her her money back because he had to get his stomach pumped three times. It's that bad.
Mr. Krabs was also shown making a terrible dinner once, which came to life and tried to eat him and some customers ("Squilliam Returns"). In the same episode we learn that he only cleaned the bathrooms on the S.S. Gourmet — but that he was the head chef on the S.S Diarrhea.
In the episode "Something Smells", Spongebob wants to eat a ice cream sundae on Sunday but he doesn't have any ice cream. Not wanting to give up on his plans he uses the next best thing - ketchup. For his special sundae, he can't use just bananas or cherries, no he uses freshly chopped onions. And finally, he tops it off with the shriveled peanuts he was growing on the windowsill along with the dirt he grew them in. No wonder it gave him bad breath.
Both of the girls on Teen Titans are lethal chefs, but whereas Starfire might be a good cook by Tamaranean standards, Raven is just plain terrible. It does not cheer her up at all when the alien on the team is the only one who enjoys her pancakes. The boys don't fare much better. Beast Boy is a strict vegetarian whose dishes are 90% tofu, while Cyborg is an avid carnivore. Their fridge has a strange, blue, living substance in it (that apparently tastes quite nice). In one of the episodes of Teen Titans Go!, Starfire is seen cooking food in a toilet.
Heffer Wolf on Rocko's Modern Life is a variation: while the meal he cooks for himself and Rocko in one episode tastes decent enough, it looks disgusting, is made from thoroughly unappetizing ingredients, and actually tries to crawl away from his plate at one point.
Rocko: Heff! This is bonza! What's in it?
Heffer: Well, let's see, there's...pickled banana shavings, gym socks, canned haggis, beetle bladders, real processed head cheese, saltpeter, reconstituted corn sweat, the finest barley and hops...*stops food from moving*...Hmm, now where was I? Potash, sulfur, monosodium glutamate, and vegetable cartilage as a binding agent!
The one time that Chowder decided to make a dish without the assistance of master chef Mung Daal, he accidentally dumped a whole bottle of poison in it, and then unknowingly tried to sell it on the streets. It even managed to burp out the warning "You... will... die!" when Mung was almost forced to taste-test it. He manages to redeem himself in the Series Finale, although everyone else is scared to try the food he made due to it being a Mess on a Plate.
Dave from Dave the Barbarian is actually considered to be a good cook, however he has an episode where Dave lived out his dream of running a bistro, the term "Lethal Chef" got taken to a new level when he used a cursed cookbook called "The Cuisinum Mysterium Cookbook" to help him — the recipes are cursed (the food comes alive and takes on a life of its own) and later on while making "Armageddon Souflé" the souflé comes to life and becomes a rampaging monster dessert.
Arthur's grandmother probably wouldn't be such a bad cook if she weren't distracted by the other things she tries to do at the same time. (Buster Baxter gobbles her cookies right down, though.)
Her son is no better, in one episode where Timmy tries to cook, it exploded.
Jorgen once made pizza with topping that include grenades, landmines, and barbwire's, and yes it explodes in your face. The Pixies made a pizza with money on it and you vomit money when you eat it. The Anti-Fairies have a Friday the 13th which causes bad luck when you eat it.
Catscratch has Gordon (being Scottish and all) but Waffle managed to do worse in the episode where he was asked to make the soup and used the wrong book- instead of using the recipe book he used the book of the dead and zombies rose from their graves because of this.
Johnny Bravo has Pops, the owner of a local diner who uses all sorts of strange things in his dishes, including possums and bald eagles. When Johnny runs in desperate for hair gel because Mr. Kevin's triple-strength hair tonic has been discontinued and is nowhere to be found in town, Pops responds with a cheerful: "Sure! Mr. Kevin's is the main ingredient in my Five-Alarm Chili!"
A slight twist was done in The Adventures of Teddy Ruxpin. Everybody hated Grubby the Octopede's food, but that was because he always used tree root as a main ingredient: A favored taste for Octopedes but disliked by everybody else. His root stew in particular was also literally lethal at times, in that it made a great form of ammunition which quickly became a standard weapon for the heroes. Subverted once, however, in an episode where it turned out that root beer is the one recipe where roots are actually tasty to non-Octopedes.
A running gag in The Weekenders is Tino's mother "experimenting" with healthy foods...with disastrous results. Tino often tries to avoid getting a parental lecture by commenting on the food instead with comments questioning the ingredients and sometimes even implying that the food is alive. Case in point: Tino and his friends once cheerfully (so to speak) ate pot scrubbers because they thought they were cookies she had made. They don't find out the truth until after.
One episode of Recess has Gretchen talking about Tomato Surprise (no relation). She later uses the Tomato Surprise to destroy the hinges and the lock on a door so she and the rest of the gang can free TJ.
Gretchen: The tomato surprise isn't without its useful properties. TJ: You mean this stuff is safe to eat? Gretchen: No. I mean if you let it age, it can burn a hole through a concrete floor. Vince:(inserts spoon into Tomato Surprise and it dissolves) It doesn't have too far to go.
The Tomato Surprise turns out to have an even more surprising use in the Halloween Episode - its acidic enough to wipe out a whole room full of zombies.
Subverted in the animated version of The Tick. The Breadmaster's baked goods (or as Tick puts it, "Baked Bads!") are intended to be dangerous (bread bombs that demolish buildings by expanding to enormous size, gingerbread men that rob banks,) although when Tick samples the first bread bomb, he comments, "This is actually quite good!"
In The Replacements, about the only thing that omnicompetent superspy Agent K can't do is cook; in one episode her husband builds an indestructible house for the family's pet mule out of K's breakfast bars.
Book: Cut Carrots (Mickey cuts some carrots) Book: Whole Carrots (Mickey takes the cut carrots and glues them back together)
While not a lethal chef per se, Johnny Test's father loves to cook meatloaf and though he loves the resulting meals, it's next to indigestible for anyone else. His attempts to bake healthy cookies taste like dirt according to Johnny. His dad forces him to taste dirt for a better comparison, forcing him to admit he stands corrected - dirt tastes better.
In G.I. Joe, Heavy Duty takes this to another level; he likes to use grenades to barbecue. This is an intentional contrast to his cousin, world class chef and gourmet Roadblock.
The episode "Raise the Flagg!" features Cobra mess cook B.A. LaCarre, who once gave a squad of Strato-Vipers ptomaine poisoning.
Chef Hatchet's job is to deliberately make terrible food for the campers. He'll actually make some pretty good food if it's for himself and/or Chris, or if the challenge calls for it (such as in "The Big Sleep", where the challenge is to see who can stay awake the longest after everybody had just eaten a huge turkey dinner).
In the episode "Who Can You Trust?", two contestants have to prepare blowfish to feed to a teammate. While Bridgette makes a perfectly edible meal (even presented as sushi rolls), Lindsay made a glob which sent Trent to the infirmary. He survived (don't ask us how).
One of the competitions in Total Drama Revenge of the Island involved the contestants finding food in the radiated island and cooking it. All four dishes were repulsive in different ways, and only one was edible in the end. During the preparation portion of the contest, Zoey's salad actively tried to kill her.
The Peculiar Purple Pieman from Porcupine Peak. When on a cooking show, his own oven groaned at the thought of baking his cookies, and one taste of his entry had the judge calling for a doctor, an ambulance, and the Marines. Fortunately, Strawberry's cooking was the antidote.
Other specials suggest his baking is so bad, Even the Rats Won't Touch It, and he knows it. In one, he tries to set a trap on a road for the heroine using pies that that turned out like super-glue. (Naturally, he only ends up trapping himself.) In anther episode, he suggests using them to bait a trap for a wild beast; after Sour Grapes expresses a small expression of doubt, he admits that's a bad idea.
Mr. Beastly once tried to make cookies by following the instructions on Grams Bear's cooking show. Despite making an utter mockery of the recipe, the lone cookie he manages to make comes out of the oven perfectly fine. And fifty feet tall. The next time we see him, his monster cookie is chasing him across the landscape. Of course, we never learn if the cookie is actually edible or not, but it's probably safe to say that only Godzilla could answer that question.
An evil pieman named Sour Sam created some apple pies that make whomever eats one become grumpier than even Grumpy Bear... apparently, Tenderheart was one of the victims. but if it weren't for Grams' Happy Apple Pies.....
June of KaBlam! is such a terrible cook that she had to be kicked out of her scouting troop because of this.
Bugs Bunny tends to do this on purpose. "Wild Turkey Surprise" consisted of a small powder keg and two sticks of dynamite, arranged and dressed up to look kinda like a turkey. The surprise? He lights the fuses. Why such a delicacy? He was feeding a Tasmanian Devil—that would otherwise have had Bugs for lunch.
Morgana McCawber is an example. Having come straight from Monster Mash land, most of her dishes look like they came straight from The Nightmare Before Christmas, looking quite unpleasant and almost always still moving. Oddly however, in-universe, the only one who ever has any problem with this is Darkwing himself.
Launchpad is also an example; in "Can't Bayou Love", he bakes brownies which immediately send Darkwing to the water cooler for a long drink. However, Jumbalaya Jake's alligator, Gumbo, finds them tasty.
Peter Griffin from Family Guy is a literal version of this trope: In an episode where he starts his own restaurant, it was revealed that the last time he made food, he baked muffins that blew up the heads of people who ate it, which was also implied to have shut down his business.
The lunch lady at Stanley and Mary-Jane's school in Staines Down Drains. She's called Typhoid Mary for a reason.
Apple Bloom and Sweetie Belle, being kids, clearly aren't up to the task of cooking just yet. Apple Bloom's attempt at making cupcakes in "Call of the Cutie" produces oddly shaped, half-burned lumps that Pinkie Pie says "look much better than the last batch" and a big mess in the kitchen. In "Sisterhooves Social", Sweetie Belle tries to make Rarity breakfast in bed and manages to completely carbonize everything, including the juice and a bowl of what Rarity guesses to be applesauce. "Nope, toast!"
In "Applebuck Season", Applejack becomes one after working so hard at the farm (several days in a row, with no time to sleep) that she's delirious and mishears every ingredient Pinkie Pie reads off to her. They end up making "muffins" out of potato chips, soda, lemon juice, and worms. Oddly, they somehow still come out looking (and apparently tasting) like muffins, and nobody notices until it makes them all sick, including Pinkie Pie, who had no problem eating the above mentioned cupcakes made by Apple Bloom. Spike loved them, though. It's also stated that she's normally a very good baker.
Oscar Proud is constantly shown to be this in regards to his food product "Proud Snacks", resulting in the person ingesting it either choking, getting cramps, or simply just falling extremely sick. In fact, of all the people on the show who've had his snacks, only one is explicitly shown to enjoy his snacks, a kid who is Wise Beyond His Years. How Oscar continues to run his business despite it clearly being unliked by virtually every single person in America is unknown.
Jacob from Motorcity. Chuck still eats his mayonnaise muffins, even if he can't stand them.
In The Powerpuff Girls, the Professor is an okay cook, except when he tries to cook chili. A flashback in the episode where he tries to do so for a chili cookoff reveals that the last year's attempt caused a disaster, and the current attempt doesn't seem any more promising. After adding Chemical X to it, it tastes good, but still causes a disaster, in the form of a methane monster.
In the Peanuts animated special It's the Easter Beagle, Charlie Brown, Peppermint Patty tries to teach Marcie how to make Easter eggs, but Marcie can't get a handle on how to prepare the eggs. First she fries them. Next she tries cooking them on a waffle iron, then a toaster, and then putting them in the oven. Finally, with help from Patty, she boils them... but cracks them open first, resulting in "egg soup".
In the Angry Birds Toons episode "Cordon Bleugh", Matilda makes soup for the other birds. The soup is a chunky brown liquid thats so repulsive, it kills plants. Naturally the other birds hate it, which depresses Matilda. When she dumps it off a cliff, it lands on some pigs. The pigs lick it up and love it, making her happy again.
Implied for Jeremie Belpois of Code Lyoko in "Triple Trouble". He informs Odd that he has a surprise for him and Odd states that he hopes it's not food because Jeremie can't cook. And considering Odd is a bottomless pit normally, that says a LOT.
Fireman Sam had a Running Gag in Elvis usually being the designated chef at Pontypanty's fire station. Usually something went wrong before anyone could actually eat it, but the characters often talk about how horrible his cooking is. Sam also tried at least once to build an elaborate machine to get around the problem, but it only made things worse. Of course, given that neither Sam nor Station Officer Steele ever try their hand at cooking themselves one can only imagine how much worse they are.