Sora Hasegawa in Ah! My Goddess (in the manga, her nickname is "The Chef Assassin"). Fortunately, she got better, thanks to Belldandy. However, in the TV series, she was actually a great cook, but suffered a Heroic BSoD whenever asked to cook for an audience, causing her skills to deteriorate. This tied into the plot of the episode, where she had performance-anxiety issues about a go-kart race for NIT's Auto Club. Again, Belldandy, being the kind of "person" she is, helped Sora get (heh) back on track.
In A.I. Love You, Number Thirty's experience of food is limited to having seen pictures of finished recipes in books, and her attempts to reproduce them fail because she has no idea that they're supposed to be made of edible substances. Of course, being a robot, she had no sense of taste. This get fixed fairly quickly when it's discovered, however, making Thirty (with a little training) a decent, non-lethal cook.
Any time Baikinman tries to cook a character's specialty meal, he'll butcher it horribly, making Dokinchan, who he normally makes the food for, upset at him even more than when he refuses to make it (his fish broth was sickly green and still had bones and scales in it, despite being made out of katsuobushi, which dissolves into a clear brown color).
Komaki-chan tries her best to follow in Tekkanomaki-chan's footsteps. Unfortunately for her, the tuna sushi she makes has too much vinegar in the badly cooled and mixed rice, and is overloaded in the sushi until it burts and leaks out of the nori.
Finally, Horroman flip flops between being a horrible chef and an okay one. When he makes a simple recipe with no specific motif (like a rice omlette or cooked vegetables), they turn out edible. However, when he decides to learn how to make the specialty item of another character, he'll butcher the recipe horribly. The unfortunate part about Horroman's cooking is that he uses it as a way to get to Dokinchan's heart...which works out for him about as well as it does for Baikinman.
Asebi from Ben-To is an odd variation of this trope. Her friend acts as though she's one, and given her credentials at inadvertently causing bad luck you would expect it. But when the main character tries her food he finds it looks perfectly nice, has expected texture and smell and also tastes fine... If not for the minute detail that nothing she makes tastes like it's supposed to. Her fried pork tastes like fresh banana. Her boiled broccoli tastes like honey. The spiced prawns have no taste at all. Even perfectly ordinary rice ends up tasting strongly of coriander for some bizarre reason.
In Berserk Farnese cant cook to save her life, and one time she tried helping with dinner she poisoned Isidro and Puck. This does make sense considering shes a noble girl and would of course suck at servants work, Farneses half brother Serpico on the other hand is a Supreme Chef.
Black Butler has Bard, whose idea of cooking usually involves flamethrowers, meaning there's a Running Gag of Sebastian having to do damage control. Though during the cricket tournament, he actually weaponizes this, switching the meat pie Bard brought along for the rest of the Phantomhive household with one meant for the opposing team, giving them food poisoning and getting them disqualified.
From Black Cat, Professor Tearju is such an awful cook that when Train and Sven opened the door to her home, they were completely overwhelmed by the horrific smell. Professor Tearju is a bit of a klutz, so when she trips, and spills the resulting mess on Sven's hat, he starts screaming that his hat is covered in living puke. Hilarity ensues.
Claire's cooking usually ends up mostly resembling charcoal. Her cat likes it, though. The cat is a flame spirit.
Fianna normally adds sleeping medicine so her unfortunate victim never really notices. However, once in a cooking duel when she made food that could knock someone out she claimed that was actually the point, to defeat her opponent.
In the Blue Exorcist anime, Mephisto's attempt at breakfast is red and bubbly, and causes Rin to shoot a puff of steam from his mouth and pass out.
Tamako Daikawa of Boku Girl is such a lethal chef that not only is her cooking censored by mosaic, but when Loki feeds some to her crow minion, it explodes and prompts Loki to comment on its viability as a bio-weapon. When Nanatarou eats it, he undergoes Rapid Aging.
In Cardcaptor Sakura, Li Meiling is amazing at cooking Chinese dishes but hopeless at Western bakery - so much that her inability to bake a cake becomes a running gag. Touya talks about Sakura's cooking as if she were a Lethal Chef, but given the fact several characters with working taste buds enjoy her cooking, he is clearly just messing around with her.
In Charlotte, Ayumi's rice omelette doesn't seem too tasty to Yu when he tries it out. But he forces himself to eat it anyway.
Chrono Crusade's Rosette Christopher is one of these. As a child she baked a batch of cookies so bad it caused Chrono to foam at the mouth. She later improved (she was accepted as cook in public kitchen, even Chrono says that when her soup looks horrible, the taste is decent).
Cecile Croomy of Code Geass sort of qualifies; her cooking isn't lethal so much as a crime against the culinary arts due to her experimenting and mixing various ingredients. Some such examples include onigiri (riceballs) with blueberry jam in the center and sandwiches with ginger, sugar, and wasabi added for flavoring. She tends to get away with it because between her co-workers, Suzaku is far too nice to say anything and Lloyd's so brutally honest that she tends to ignore his criticism.
Risa from DNAngel is a terrible cook, however, Takeshi doesn't hesitate to tell her so. He also tells her that she'll never improve if she takes advantage of a nice guy like Daisuke, who'll only eat her food to spare her feelings.
In Da Capo, Junichi's adoptive sister Nemu is considered to be a lethal chef, at least for the first season. Her cooking was so bad that Junichi even calls her a "Murderous Chef" behind her back.
Variation: Ren, in a cooking contest in DearS, causes humans' eyes to bleed... but the other DearS love it.
In Detective Conan, the direct reason for Kogoro and Eri's separation is the latter's cooking was too awful. Actually, she once tried to cook for him after a Shoot the Hostage situation and he called her out for it way more harshly than he intended. Even Shinichi knows how awful Eri's cooking is.
Yuuko Kamiya, Tai and Kari's mother in the dub of Digimon Adventure is characterised as a terrible cooker with a fondness for cooking weird foods. In the second part of the Digimon movie, her "beef jerky shakes" almost kill Izzy. Compare it to the single movie "Our War Game" in Japan where Koshirou simply has a Potty Emergency from drinking Oolong tea.
Hina in Domestic Girlfriend can't manage much more than microwaving leftovers. Despite her efforts, any real attempt at cooking goes horribly wrong and is lucky if it is even edible.
In Dragon Ball Super we find out that Vegeta, Prince of All Saiyans, cannot cook to save his life. He can't even break eggs without the stupid things shattering in his hands. The only thing he can cook is instant ramen noodles.
Rath of Dragon Knights is a rather horrible cook. The soup he made for Cesia when she was sick included hot sauce and other improbable ingredients and tasted awful.
Dr. Stone: It's a Running Gag that despite Senku's encyclopedic knowledge of chemistry allowing him to make any food from scratch, he's actually a rather terrible cook (plus his ingredients are rather low-quality). However, it's also a Running Gag that the primitive people of the Stone World love everything he makes, because they barely have any cooking whatsoever. It's the modern people who are the picky eaters.
In Durarara!!, the author drew up a picture of all the girls involved in a cooking contest. While some of them did really well, others...did not. The second worst was Anri, who managed to get a worse score than the girl without a head to taste with. Then there's Emilia, who got a score of -20... but she seemed to be under the impression that she was supposed to be making a bomb.
Nana of Elfen Lied, having been raised in a lab, is a terrible cook, often burning the food she makes. Oh, and watch out when she handles a cleaver too...
Comes in two forms in Ergo Proxy. Pino is a robot who doesn't eat and as such has no idea how to make food palatable to humans. In episode 16, Re-l shows a different form of this, failing to boil pasta successfully. In her case, it's the consequence of a life lived in a seemingly Utopian dome with all work done by robotic servants, and perhaps a bit of Feminine Women Can Cook as well.
Esper Mami, apart from being generally a klutz, is also a lethal cook. She blacks out when tasting her own "food" the first time she tries cooking for her best friend Takahata while his parents are away, which might just save his life. Later every time she suggests cooking, her friends just shoot the idea down. Although she does take a special crash course so that she can cook a good meal for Takahata and her father while they're on vacation.
Subverted beautifully by NaoSadatsuka. The dish she presents to the judges at the Fall Classic is not only extremely vile looking, but the smell of it is so bad that just about flattens everyone within the building. However, one incredibly brave judge tries it (despite being on the verge of vomiting from the smell alone)...and it's so delicious that she can't stop eating it. This prompts the other judges to follow suit, and they proceed to give her the high score up until that point.
Played straight with Tamako, Soma's late mother. In spite of being the daughter of a restaurant owner, Tamako was a horrible chef. She had the tendency to mix bizarre ingredients her husband wouldn't even think of. Her father was used to her failure dishes, although there were times when she made decent dishes, especially the fried rice. Strangely the customers viewed this to be amusing, placing bets on whether Tamako's dish would be a hit or a fail.
In the manga of Fruits Basket, Kazuma Sohma (Kyo's adoptive father, and a rare male example) is extremely inept at cooking, though not through lack of effort (he even has trouble making tea). This had the side effect of making Kyo a halfway-decent cook; he had to learn just to survive. Yuki, is also horrible at cooking.
Lieutenant-Commander Andrei Kalinin has his special borscht (an eastern-European beet soup) — a recipe made by his late wife that he has spent years of experimentation to successfully replicate, including on-the-second stirring, pH sampling, and adding such outlandish components as cocoa powder and miso paste. Said borscht is sufficiently gruesome (Tessa states it tastes like "hot Dr. Pepper") to scare away even intractable stoic Sōsuke, which was the whole point — Kalinin's wife was rather vindictive of his prioritizing his career over her. Kalinin himself, however, is completely oblivious to this and finds it delicious.
Sōsuke himself is also shown to be a rather Lethal Chef (at least in the manga). Most of it stems from his lack of common sense, which results in him cooking rice in a rice cooker... over a fire. Indoors. Which causes the others to faint from the fumes. And in the end, he misinterprets Kaname's "a pinch of salt" as being a whole handful of salt.
Miaka Yuuki in Fushigi Yuugi. She becomes better halfway through the second arc of the manga, but before she does, Taka lies about it to her. And she never tastes it.
Sakurazaki sisters in Futakoi, what with being so aristocratic. Though with an effort they improved their cooking skills, trying both for their father's "exam checklist" and Nozomu.
Sara in Futakoi Alternative once served up a pitch black "hot cake" that had another character shoot flames out his mouth when he had some. She also ruined a dish her twin sister was trying to make by dumping what looks like the entire contents of the fridge and garbage into the pan.
Asuka from Future GPX Cyber Formula. At one time, she makes parsley and durian juice for Hayato because she hears that he is lacking in vitamins, but he doesn't want it due to the smell...so she drinks the juice instead, and then cries that it was bitter and faints from drinking her own "concoction".
Otae Shimura from Gintama can only cook tamagoyaki, but it's so inedible that it actually gives Gintoki and Kondou (and later Otsuu, too)amnesia at one point when she feeds it to them, and is reputed to be the cause of her brother's bad eyesight. And yet, she never seems to understand just how lethal it is and continues to serve it no matter what. Once she was making sushi with the rest of the cast. No fire was involved but somehow the sushi turned into ashes moments later. Tamagoyaki ashes.
The super ditz in Girls Saurus DX said that when cooking she could mix up sugar and potassium cyanide!
In Girls und Panzer's Motto Love Love Sakusen spin-off manga, Darjeeling is portrayed this way. She serves her team mates Assam and Orange Pekoe an inedible meal, then invites the Ooarai Girls for the same. Yukari even wonders if it's an MRE.
While in the library in episode 4 of Gourmet Girl Graffiti, Ryou is told her grandmother used to borrow a lot of beginner's cookbooks from there. She calls her aunt, who tells her that her grandmother used to actually be a lousy cook while raising her and Ryou's mother. She is then told that her grandmother only seriously started learning how to cook after she started to watch Ryou more.
The hot pot in Haganai is black boiling, causes a Vomit Indiscretion Shot, and as Rika puts it (visibly nauseated) "The closest flavor to this in my memory banks is... RUBBING ALCOHOL!"
Sanzenin Nagi in Hayate the Combat Butler. One of her attempts would probably have turned out pretty well... had she not confused detergent for flavoring oil. Even attempting to make a cup of tea usually destroys the whole kitchen.
She tries to serve soup to a large party. Nagi is chopping up the most random things (daikon, chocolate, fish, oranges, what looks like raw pork, mushrooms, barnacles...). Note that she is tossing everything into a pot, not caring to look what she's chopping up. And because Hayate is such a Dogged Nice Guy, he just has to taste it, vomit it up, and quickly make something not only edible, but quite delicious, just so Nagi won't embarrass herself.
England from Hetalia: Axis Powers loves to cook, but the food he makes is terrible to the point that Austria even tells him that he's sorry for England for having such horrible cuisine. One comic jokes that his lack of taste is the reason America's cuisine is what it is now; in another, England does NOT like how America tells him his scones suck and mauls him in front of everyone.
The title character of High School Ninja Girl, Otonashi-san mostly joined the cooking club so she could eat, as her attempts to actually cook tend to be typical of this trope. Fortunately she's self-aware enough about it that she makes sure to taste test her food by tricking her rival Shimura into eating it first. Frotunately, the boy she actually desires to cook for has an iron stomach and can eat her cooking without issue.
In one episode of Higurashi: When They Cry, Keiichi's parents are out of town, and he has to cook for himself. He almost burns the house down.
Both Hagu and Yamada from Honey and Clover are terrible cooks with chocolate and mushroom curry, chocolate mintkin (a pumpkin topped with chocolate mint icecream), and Grapefruit Pilaf. In an interesting subversion, the manga's English language editor made her own grapefruit pilaf, thought it was nice, and published the recipe.
It is apparently shown in season 2 that her lack of common sense is a major cause of her horrendous cooking skills. While teaching her how to cook, Houki, Charlotte and the latter's roommate, Laura, all get sick from her attempts to make the food look better. Later, when Rin to teaches her how to make sweet & sour pork, Cecilia decides to use her IS's laser upon hearing Rin's advice that Chinese cooking is all about "firepower". Much explosion ensues.
Seraphim from Is This a Zombie? brings this trope Up to Eleven with a vat of bubbling purple... stuff. Anything put in it will melt afterwards, like spoons or chopsticks. When attention focuses back on the cauldron, the cauldron is empty and has a huge hole in it... as well as the table... and the floor...
On the next season "Of the Dead", her cooking prowess has Sarasvati make the kitchen forbidden to her. Aikawa still asks for food made by Seraphim and gets a steak as result. Said steak has sparks that make it look pretty radioactive, but Aikawa still eats it almost melting the fork he used, and the steak manages to explode after being eaten, leaving Aikawa barely conscious. He asks for another, making Seraphim blush and show her "caring" side. The steak in question had nitroglycerin as a secret ingredient; thankfully Aikawa being unable to die can avoid the "Lethal" part of Seraphim's cooking.
In Kaleido Star, Rosetta Passel is not only a Lethal Chef, but is quite incompetent in anything related to housework for quite a while. At the same time, Layla Hamilton seems to have difficulty brewing coffee even with a machine, relying on her maid's advice and even then screwing it up. And also, Julie complains that her best friend Charlotte is too fond of using salt on everything.
During the curry-making contest in KanColle, Hiei adds... something to her sister Kongou's curry, hoping to improve it. Undeterred by the fact that the formerly orange dish has turned an evil shade of purple-blue, they give it a taste - only to freeze in shock, turn several vibrant colors, and collapse to the ground in perfect unison.
Carrera and Anju in Karin attempt to make a normal human dinner when Karin brings her Muggle friend Maki over for the night. Since they're both vampires (and literally don't have any sense of taste for anything except blood) and don't actually eat human food, they don't know how to cook it either (Karin, being an "unvampire", is the only one that cooks) and the results only look edible.
In episode 5 of Kotoura-san, the contrast between Hiyori's "cooking" with Haruka's (good but not yet Supreme Chef levels, as Daichi commented) is clear. Manabe just calls the hamburger steak she made—shaped wrongly and emitting a purple aura—poison. Then in episode 6, she made a meal so bad, that it had not only infernally bad taste, but was also mind-altering: it made her want to get frisky right now first with Manabe, then with Haruka. Manabe in delirium mistook a vase for Haruka.
Kuroko's Basketball: Riko Aida's food is so bad, people pass out after eating it a couple of minutes later.
Kyouka produces food that only Yuka is able to eat without ill effect.
Subverted in episode 7. A pair of former assassin siblings open a restaurant, where their cooking nearly kills all of their customers, until Chika realizes that the cooking is too good to be consumed by normal humans.
Hikari in Lamune likes her food really spicy... leading to those familiar with her to fear any time she decides to cook. Also results in a humorous incident during the Class Trip when the group leaves the curry pot unattended and she goes to take a look...
The "looks horrible, tastes fine" variant occurs in The Law of Ueki: while Mori Ai's cooking looks unappetizing (it seems to contain live, squirming purple octopus tentacles), it actually tastes quite good and doesn't have any ill effects on the eater.
Millenium Fera Nocturne a.k.a. Milly on Lost Universe is a variant on this: she's a great cook, but always causes a massive explosion in the kitchen whenever she prepares a meal, much to the consternation of Canal (who, being a Spaceship Girl, is also less than happy about having a part of her body blow up every time Milly wants to make a pie — not to mention how expensive it is for them to have to repair it all the time).
A variation occurs in Love Hina. Naru's cooking consistently looks inedible, but just as consistently tastes good.
In Love Roma Negi cannot cook to save her life, even her boyfriend claims her cooking brings back bad memories.
Sweetly subverted in The Lucifer and Biscuit Hammer. Sami is actually well aware of how terrible her cooking is and is even vocal about it. Yuhi, on the other hand, eats every bite and tells her it's delicious. He's actually lying to spare her feelings; he finds her cooking to be quite unbearable. But seeing him eat it makes her happy, so to him, it's worth it. Awww.
Lampshaded in Lucky Star when it's revealed Kagami is the worse chef of the Hiiragi twins, as she and Tsukasa take turns making their lunches:
Konata: What? Kagami, are you the kind that can make pots explode when you cook?
Maburaho contains an episode where Rin's "cooking" is forced down to make her feel better.
Sawanaguchi Sae, in Magic User's Club, lives in Tokyo with her older sister Saki. Sae usually does the cooking. One time in the OVA she comes home and finds Saki trying to cook; she asks what she's making, and Saki says, "Tomato Stew." Sae asks why she's making it out of red chili paste and Saki asks, "What's that?" At which point Sae says, "I think you should let me do the cooking."
The boss of the Gaba thieves in Magical Circle Guru-Guru is a Lethal Chef who loves to cook. To make it worse, criticizing his cooking will cause him to become lethal in more traditional ways. He allows Nike to become his disciple solely on the basis of making Kukuri teach him to cook better.
Subverted in Magical Pokaan: the first time we see the girls eating Aiko's food, they carefully taste it... and right when you expect them to hurl, they say "Average".
In contrast to Supreme Chef Usui, Misaki in Maid-Sama! can't even make riceballs correctly. Fortunately her few attempts at cooking stop short of being actually toxic, because Usui insists on eating it anyhow (and then complains about it).
Yako's mother from Majin Tantei Nougami Neuro. Yako is just as famous for her immense appetite as she is for being a detective, yet even she is afraid of the meals her mother cooks. Some examples of how disastrous her cooking can get:
Her idea of preparing is to visit a hardware store. Sure, some tools can be used for cooking, but a power drill, hacksaw and chainsaw don't really suit cooking.
She apparently forgets that some of the ingredients she puts in a cake (egg shells, whole chicken wings, fish bait, balloons, oil paint) are inedible. It starts to smell like rubber when it's baking. Then for the icing, she mixes in nitroglycerin. Neuro provided the icing recipe. The cake was later re-used as garden blocks that created the following effects: Flowers wilt in half a day, the cake didn't rot after ten years had passed, radiation was detected from the Katsuragi family garden.
For a town carnival, she brewed some pork soup. The color of the soup was silver and 95% of the tasters were hospitalized.
Her Valentine's Day chocolate looked like a chunk of steel and smelled like a dead animal.
The various women pursuing Akito in Martian Successor Nadesico vie to impress him through cooking; this is doubly ironic, as not only are they all borderline lethal chefs, but Akito himself is a restaurant quality cook. The first time they tried to cook for him, the head chef on the Nadesico quarantined the kitchen as a biohazard for a while afterwards. Ryoko eventually wises up and serves Akito some of his own cooking. He deems it "pretty good" before she points out that he's the one who just cooked it.
Inspired by a poll of what qualities boys desire most, Luna tries her hand at cooking in the Mega Man Star Force anime to win MegaMan's affection. The terrifying results lead her to seek training from Geo's mom. It doesn't help; fortunately for Geo, she's soon distracted when "cleaning skill" wins the next poll. She comes back to cooking at some point before the sequel series Tribe starts, and makes actual progress this time — in fact, the food she brings turns out to be the only reason anyone comes to Hyde's art classes.
Kana in Minami-ke, to the extent that she can use her being required to cook as a threat. She did spend an entire episode trying to get better in Okawari, though taste testers Touma and Mako-chan got very well acquainted with the bathroom in the process.
Downplayed in Mission: Yozakura Family. Mutsumi is a good cook, the problem is that the Yozakura recipes for food and medicine tend to be nightmarish to behold. One ancestral manju bun recipe she tries involves adding potassium cyanide, puffer fish, and hydrochloric acid into a blender, and the result comes out looking like something out of the Cthulhu Mythos. In fact, "feeling like you're at the verge of death" after eating it is in the recipe. Tasting it causes Nanao's neck to mutate and turn purple, while Shion's scanners classify it as a deadly weapon. Even Kyoichiro is knocked out for weeks afterward.
Kimihito is clearly the only character who can cook, but most of the others either aren't interested in cooking, don't know how to cook, or serve up something bland and uninterestingnote Though it is implied that Centorea is a competent cook, her taste buds are far more sensitive than the rest of the cast's because she's an herbivore, meaning they tend to find her food very bland. Also, as stated she's an herbivore while the rest of the cast are either omnivores or in Miia's case a carnivore and thus don't find her tendency to just serve salads to be terribly interesting. Miia, however, is firmly in lethal chef territory, with a bad habit of cooking fish skeletons into every dish, and serving up pots full of mysterious smoking purple "stuff". While it's meant to be justified since her species has a poor sense of taste and she can't know how bad her cooking is, one notorious meal she served up knocked someone unconscious through smell alone. She also has a tendency to toss in ingredients just because they look or sound similar to what she's making: she tried making white rice and added white onion, white fish, and white chocolate to feed to Kimihito when he got sick. Fortunately for him, Suu ate it before Miia got the chance.
The anime adaptation of the series somehow makes Miia an even worse cook: in the manga, Suu is shown to be the only one who can safely eat Miia's cooking thanks to her innate immunity to poison - she was originally attracted to Kimihito's house by the smell given off from Miia's first cooking disaster. In the anime, though, Suu showed up before that and even she was poisoned by Miia's cooking.
In the third season of Monster Rancher, it's revealed that Golem dreams of becoming a chef and opening his own restaurant. Unfortunately, as a creature that eats rocks and drinks sand, his recipes need a lot of work.
Moon Led Journey Across Another World: Mio has a number of problems when she first tries cooking, first and foremost among them being that as an Extreme Omnivore, she hasn't got her head around the idea everyone else does not see everything in sight as edible: when she tries making curry and rice, the result (which among other things includes emeralds on the assumption that the "green" she's seen in it must be the most delicious gems) incapacitates everyone else who eats it and melts the pot. She at least understands the basic idea of toast, heating bread over a weak flame, but her idea of a "weak flame" burns it so badly there's nothing left.
Musuko ga Kawaikute Shikataganai Mazoku no Hahaoya: Lorem started out as being absolutely terrible at making food, with several of her earlier attempts being completely inedible and so horrible to look at they were covered by a mosaic. Even when she genuinely put in her greatest efforts, the best she could do was make a somewhat edible carrot paste for Gospel, and even then the only reason he ate it was because he wanted to make her happy. That said, she's been constantly "training" since then to improve her skills, and while she's still nowhere near a Supreme Chef, by chapter 69.5 she's reached the point where she can make food that can be enjoyed by other people, such as Gospel's birthday cake.
In the Cooking Duel in My-HiME, none of the three teams succeeds in producing an edible cake, resulting in the judges being hospitalized. Mai's team comes closest (because Mai herself is actually a competent cook), but Shiho ruins it by getting too excited and smashing her face into the cake before it's given away for tasting.
My Monster Secret: Youko, Aizawa, and Shiho are tasked with making curry as part of a home economics class. The end result is Shiho being knocked unconscious and Youko and Aizawa trying to dump "what once was curry" out of the classroom window. A later chapter shows that Shiho is similarly bad at candy making, as her creation consisted entirely of a rotten banana dipped in chocolate.
Arika in the (subverted) Beach Episode in My-Otome. Upon seeing her food, Shiho initially gives it zero points, but after Arika tricks her into tasting it (with disastrous results), the rating is dropped to -10 (negative ten) points.
Grandis from Nadia: The Secret of Blue Water is a subversion. Her cooking looks absolutely well beyond amateurish and more in the realm of horrific, but it's actually quite good.
Nana of Nana to Kaoru tries her hand at Valentine's Day chocolate for her totally-just-a-friend Kaoru. Unfortunately, she has no idea what she's doing, given her focus on studying over cooking, and "melting chocolate" becomes "chocolate cake". Kaoru is overjoyed to receive it, but the bout of diarrhoea it causes means he has to skip school.
In one episode, Asuna bakes a cake for a teacher she has a crush on. Said cake not only has green frosting and uses a tentacle, several eyes, and a lobster claw as ingredients, but actually screams whenever on screen and bleeds when cut into. (Fortunately, it was only her "practice" cake, and the second one she cooks — and which she really intends to serve — is bakery-perfect.)
In the Negima!? anime, Takamichi becomes obsessed with making ramen, eventually inventing a ramen that makes everyone sick — even Evangeline.
Miyabi of Ninja Nonsense. Episode 6 sees her taking making dinner for the ninjas after Shinobu gets stuck at Kaede's house by a typhoon. She creates a stew that includes leeks, chicken legs, broccoli, lettuce, apples, a whole duck (complete with feathers and beak), a boot, an umbrella, and what appears to be somebody's buttocks as ingredients. She then adds pepper (actually gunpowder, but she can't tell), which causes the whole mess to explode.
Haru from Ojojojo is a downplayed example. Her food isn't bad (if a little overcooked), but fire has a habit of showing up in large quantities whenever she tries cooking.
Gramps: [After handing Haru a fire extinguisher] Also, should I call the firefighters in advance?
Luffy wastes a whole week's worth of food supplies to make a giant, inedible soup of rotten food, putting him and his friends in danger of starvation since they are in the middle of the sea.
Filler character Apis tries to show her gratitude to the Straw Hats for saving her by cooking a meal for them...the thing is, though, whatever it is she's tried to cook is burnt to charcoal status (and the cooking utensils are severely burnt after she's done preparing it), and when the crew eats a bite of it to spare Apis's feelings, they wind up chugging water to get rid of the taste (and Zoro actually changes color from eating it). Of course, Luffy is the only one who can eat the "food" with no ill effect.
In the ultimate form of irony, Sanji was this when he was a child. Years of Training from Hell under Chef Zeff changed this.
Lead Onidere character Saya's cooking is so lethal that her fellow gang members collapse, including one who experienced actual poison. It seems to run in the family, since her sister can not only drink the tea she makes, but actually enjoys it. Her food causes those who eat it to flashback to their worst pain ever (such as the aforementioned poison) and calculate how much worse Saya's cooking is. Saya's tea makes people flash back to her cooking. Half a plate was enough to take down her father (who is otherwise invincible), and constantly eating it has granted her boyfriend universal Acquired Poison Immunity.
Misty had also tried her hand at cooking when Brock was sick. It wasn't pretty. The ingrednients involve liberal doses of ketchup, chocolate syrup, and lots of enthusiasm.
May once caught a buttload of berries and blended them into Pokeblocks. The team tried them and subsequently gagged. Only a Munchlax could eat them without collapsing in pain, and she ended up catching it.
According to Meowth, Jessie is also an example: "The last time you cooked you wiped out eight of my nine lives." She apparently has a wonky sense of taste as she loved Misty's attempt at cooking and also liked eating May's "Purple Surprise" Pokeblocks.
In the Sun and Moon series, Ash and Pikachu attempted to cook when Kukui was out, but Ash really needed proper instructions, and the RotomDex's instructions left a lot to be desired... including how much salt and pepper is the right amount. Its failure to clarify what to flambé something means probably didn't help either. The result was an inedible purple mess that Pikachu didn't even attempt to eat due to the awful smell and which produced sparkles when Ash puked it out. Ash's other attempts in previous series were similarly bad. There are some foods he can prepare well, so he's not completely incompetent; but he's not good at improvising and tends to burn things.
Variation in The Prince of Tennis. Sadaharu Inui uses his horrible juices as a punishment for his teammates when they fail in training. These juices are so bad that everyone in the team (except for Shusuke Fuji, the local Extreme Omnivore) is actually terrified of receiving juice punishment.
C-ko Kotobuki in Project A-ko, who seemingly cannot tell the difference between edible and inedible ingredients; her bento has been known to contain pebbles and bottle caps. The Card Game Ani-Mayhem even had her food as a Disaster card that would merge with Akane's Cooking (see above) and produce effects not all that different from nuclear radiation, which couldn't be removed without a lot of characters with the Cooking skill, or by "sacrificing"note removing from the game a Kasumi Tendo card.
A hilarious double subversion occurs in R.O.D the TV: Sumiregawa-sensei comes home to find a fancy dinner and a beaming Michelle, her hands covered in bandages. Sensei sits down and gingerly tastes it... and to her surprise it's delicious. She praises Michelle, but Michelle corrects her, saying she had a go at cooking earlier and since that didn't go so well she ordered something instead, upon which she hands Sensei the check.
Akane Tendo in Ranma ½ is infamous for her poor cooking skills, which first debuted in the Bakusai Tenketsu arc. Unlike some examples of this trope, the reason why Akane's food looks and tastes awful is made self-evident when we actually get to see her cooking; she's impatient and easily distracted, being prone to mixing up her ingredients (not helping is that she likes to make weird culinary experiments, a trait more prominent in the anime but originating from the manga), and her usual clumsiness and "brute force over finesse" mentality follows into the kitchen—stirfried carrots containing slivers of wood from the cutting board due to how hard she was chopping, for example. Though she tries hard, by the end of the series, the best she's accomplished of her own accord has been either a block of tofu in an anime filler storynote which isn't saying much; tofu comes precooked and a single decent curry in the manga. Her food is shown as incredibly disgusting in a mundane sense, prompting gagging, pained winces, and stomach distress—only Ryoga Hibiki, who has Super Toughness and who is infatuated with her, can willingly choke down her food with few ill effects. Ranma ½fanfiction, however, has created a body of fanon that attributes far more outrageous results to her efforts.
It bears mentioning that, unlike some Lethal Chefs, even Akane can't stomach her own cooking, and the fact that she doesn't taste her efforts as she goes is suggested to be one of her many problems.
In a manga story about "love-predicting mochi", Akane buys magical ingredients for rice mochi that are supposed to mark the cook's One True Love with cherry blossom petals on their face (or a big, angry X if they're not meant to be). While the magic apparently still works, they're still terrible enough that the first instinct of anyone who eats them is to choke and smack their head with their hands as hard as possible, leading to confusion when Ryoga's hooves as a piglet are shaped exactly like cherry blossom petals.
At the start of the Ryugenzawa arc, Akane successfully cooks a decent, tasty curry, which is so out of character for her it sends the entire family into shock. However, later in that same story, she unwittingly uses a magical water that is capable of healing all wounds, and makes her soup incredibly delicious. She puts her faith in this water, so when it runs out, her rice cakes are once again potent enough to knock out a grown man.
In one late manga Filler story, Ranma actually gets the bright idea to try and use Akane's cooking as a Masochist's Meal challenge to try and earn money for Ukyō after she takes to her bed sick and Akane insists on cooking.
In the RPG videogame The Curse of the Red Cat Gang for the Super Nintendo Entertainment System, Akane's cookies and lunches are items which cause one or all enemies, respectively, to be instantly defeated.
Hinako Ninomiya is a lesser-known example. She only tries to cook once (in an attempt to impress Soun's daughters by volunteering to make breakfast), only to end up burning the food.
Ranma: I guess Akane had been cooking again? Akane: EXCUSE ME?!
Both Ryoko Mitsurugi and Azumi Kiribayashi (potentially) of Real Bout High School live up to this trope in a parody of Iron Chef. When the judges are about to taste the bento lunches made by the girls, they are stolen by Shizuma Kusanagi and consumed on the run, which causes him to turn green and vomit improbable quantities of grey foam.
Bianchi from Reborn! (2004) Her cooking is so horrendous that, as a professional assassin, it's literally her Weapon of Choice. In fact, it is referred to as an explicit superpower — anything she cooks turns into lethal poison, regardless of any other factor. As is normal for this trope, she is immune to this poison.
Retired Heroes: Saliy used to be an absolutely horrible cook, but years of practice have made her food edible.
Inner Moka (but not Outer Moka) in Rosario + Vampire is this. Her attempts to handle common kitchen utensils were incredibly dangerous (to her), and the pie she attempted to make appeared to be alive and hostile. Her second attempt, with every other girl in Tsukune's harem helping, resulted in an edible (if slightly burned) pumpkin pie, at the expense of destroying the kitchen and rendering all the other girls unconscious. Her normal cooking is so disastrous that it can send a full blood vampire to the hospital with a single bite.
In the anime adaptation of Run with the Wind, Hanako offers to cook breakfast for the Kansei track team when their usual cook Haiji is unwell. Unfortunately her cooking (which looks discoloured and has... some sort of purple fumes coming out of it) is so horrific it sends majority of the members to the bathroom and gives them a case of Color Failure. Only Kakeru and Prince are unaffected and somehow find her food delicious. Her family apparently can't bring themselves to criticise her, as she mentions they love her food and that her dad even cries whenever he eats it (obviously tears of agony, but she thinks they're Tears of Joy).
Kaoru Kamiya in Rurouni Kenshin produces rice balls that taste like mud. Sanosuke once mistook her feeding him some of her miso soup while he was asleep for poison. She even admits that she can't cook.
Kaoru:(to Kenshin, after eating some rice balls he made) Those taste bad... but you know, you're a better cook than me.
Luchs continues to consider gunpowder a staple ingredient (although Panther pioneered the technique), despite the Amusing Injuries that regularly result.
Lime's cooking regularly yields a charred thing that bounces around on the plate. Over the course of the show she improved enough to make food that Lorelei found tasty in Saber Marionette J to X. And Luchs was just as good a cook as Cherry in the Saber Marionette audio dramas, at least.
Usagi and Minako are both terrible cooks in Sailor Moon, though Usagi does manage to get a knack for curry that looks horrid but tastes really good (she first cooks this in R then does it a second time in Super S for a literal Starving Artist). She also makes some cookies which have the opposite attributes. In the anime at least, Rei can't cook, but has the sense to limit herself to instant curry.
Subverted in the second season: Sanzo's companions encounter a woman whose cooking is so notoriously bad, her meat buns are used as ammunition to fight demons. Cho Hakkai steps into the teacher role, only to see her "improved" cooking (apparently) just as lethal as ever... until the man she loves tries it anyway as a show of devotion, and finds it perfectly likeable. (Turns out, she had a rare gift to create, essentially, holy cooking — so even her good cooking is lethal to demons, which happens to include both Hakkai and his friend Sha Gojyo.)
Gojyo himself, on the other hand, is so awful a cook that it's a running gag in the series. His signature dish is 'Everything in the Fridge Curry', which is so disgusting (hot dogs and tentacles are just the visible ingredients) that the mere smell of it drives his teammates off-screen to puke. And these are guys who deal out mass death on a daily basis.
Jin in Samurai Champloo. After accidentally taking a job at an unagi stand (he had thought the "kiru" job would involve, well, killing), he cooks one for a stranger who had helped him with the eels. He burns the living Hell out of it, and she calls it "the worst thing I've ever tasted." This is part of a running gag about Jin having absolutely no aptitude for anything but kendo.
In the School Days Valentine's Day OVA, Kotonoha. Her attempt at making Valentine's Day chocolate for Makoto is an Eldritch Abomination. With tentacles. And it's alive.
Tsukamoto Tenma and Sawachika Eri from School Rumble qualify. Their rice balls led to ... bad things.
Jun, from Science Ninja Team Gatchaman, was a terrible cook — according to Jinpei. In fanon, so much so that she, herself, wouldn't eat her creations.
Pacifica Casull, the titular Scrapped Princess, a.k.a. "The Poison that will Destroy the World"... but not in fact by her dreadful cooking (her foster brother actually teases her about this...).
In The Seven Deadly Sins, Meliodas always cooks food that looks prefect but tastes absolutely disgusting. The only character who doesn't mind eating it is Hawk, a talking pig.
In Shakugan no Shana, Wilhelmina Carmel is known as The Specialist of Everything, but she can't cook to save her life. She was able to feed Shana and herself solely on melon bread, instant noodles, and other things that don't need to be cooked. She gets jealous of Chigusa for her Supreme Chef skills. Wilhelmina's attempts to improve her cooking skills end up burning the kitchen down.
In SHUFFLE!, Nerine says that all her cooking attempts ended up in disasters, including explosions. She eventually manages to make an omelette, but never managed to expand the repertoire. In the graphic novel, her father was so happy he wanted to make it a holiday.
Subverted with Asa, who are surprised despite her Tomboy personality that she is an excellent cook.
Xellos of Slayers notoriously lost a Cooking Duel by using his amazing culinary techniques to produce a stew so unpalatable as to cause its component vegetables to writhe and scream in agony. Then again, that was exactly as he intended — he was under the impression that in any sort of "duel", the point is to kill the other person. According to him.
Hikari in Special A has a habit of overexerting her strength, resulting in ingredients getting pulverized. She also overloads on the base ingredients for her dishes, which combined with the above results in a perfectly smooth rice ball dense enough to crack the floor. Oddly, for this trope, she tends to add too little seasoning - so even her curry ends up watery and bland. She also tends to blow up the kitchen. In fact later in the manga when Hikari and Finn are being held captive in Finn's castle, Finn takes Hikari to the kitchen and has her cook something. This causes an explosion which gives Kei and Ryuu a general idea of where they were. And Finn uses Hikari's food to knock out the guards.
Yor from Spy X Family is a dreadful cook. Anyone that eats her food passes out from how horrible it is, even dogs. The only one that enjoys her food is her brother Yuri, and even then he says he enjoys it while vomiting and bleeding (according to an omake, eating Yor's food since childhood, combined with her embarrassed slaps, has made Yuri resilient enough he can get hit by a truck and walk away with only a scratch). Yor does make an effort to improve after her "husband" Loid spent an entire day on the toilet (in reality a cover for a spy mission) and learns to make a single dish that doesn't make everyone sick.
In Steins;Gate, whenever Kurisu Makise cooks, Okabe will freak out & try to discourage her from in his words "destroy the lab from within". She just pick random ingredients for the food which explains the reason behind her terrible cooking. In one of the drama CD, even sending a D-mail to the past in an attempt to improve her cooking skills is proven futile, leading Okabe to feedback that Kurisu's foul cooking crosses over world lines.
Lt. Colonel Minna-Dietlinde Wilcke from Strike Witches. She has a terrible palette in general, and likes drinks that Yeager compares to engine lubricant. The other witches live in fear of her actual cooking. In one episode, Barkhorn tries some purple slop that she made and immediately vomits up a puddle of blood and passes out facedown in it.
Taken Up to Eleven in The Story of Cinderella with Charles. When he is forced to prepare supper for Cinderella's stepfamily and Duke Zaral, Charles is given a cookbook. Because he doesn't understand any of the directions, he cooks the food without them. Charles over-bakes the bread until it's burnt to a crisp. He also screws up the soup by throwing in a potato without peeling it first, dumping a whole basket of other vegetables in, and accidentally dumps in the entire containers of salt and pepper. Naturally, when Duke Zaral tastes the soup, he is disgusted - which causes him to leave early. (Though since Charles is a prince, and he's used to servants doing all the cooking for him, his cluelessness is justified.)
Ryoko is one of these. Her first attempt in cooking in the OVAs ends up bubbling up pink froth that dissolved the stove (What she was trying to make was never specified, but by the ingredients, it looked like vegetable soup). Later incidents in the OVAs and manga toned her lack of culinary skills down, but her cooking still could be divided into two categories: The ones that turned out wrong, and the ones that nobody got a chance to taste for some reason. She does have a very good excuse: As she says, she has no sense of taste whatsoever. Thus, explaining why she doesn't just taste it herself. She is quite literally incapable of tasting anything.
The manga-only character Asahi was also one of these. For some unspecified reason, she felt that food had to be extremely spicy to be flavorful, and so tended to season each helping of food she prepared with multiple tubes of wasabi.
The manga also paints Ayeka like this. One story has Tenchi falling ill due to one of her and Ryoko's fights knocking him into the lake and, to make it up to him (and to win points towards winning his heart), she attempts to make a meal and refuses to get Sasami to help. She does realize her ineptitude of it all and, in the end, gets Sasami's help. Sadly, by the time they were done, Tenchi's fine - it's Mihoshi who's sick from her attempts to get Tenchi better.
In the case of Washu, it's a different story: the Mihoshi Special shows her being unable to cook fish (which she blames on Terran stoves being too primitive; considering who we're discussing, it's decidedly possible), but when we see her in episode 8 of the OVA series, she's just as good a cook as any. It probably helps that the Mihoshi Special isn't canon.
In Tengen Toppa Gurren Lagann, Nia's cooking looks delicious — however, it is horrendous enough to knock Rossiu out of commission for the entire episode. And, since Nia is super hyper moe, nobody wants to hurt her feelings. Bizarrely, Simon and Boota genuinely enjoy her food and suffer no ill effects. An Alternate Universe adds that, had Kamina and Nia met, Kamina would've loved her food too.
Lisa Mishima from Terror in Resonance tries cooking for Nine and Twelve on one occasion to prove that she can be useful to them, and fails miserably. Twelve asserts that it's completely inedible, and after trying it herself, even Lisa admits that it's terrible.
Lampshaded openly when Rimuru figures out that this trope is being used the moment everybody else decides they're not hungry when Shion is cooking. To put it into perspective, Rimuru initially has no sense of taste due to being a slime and is still unable to stomach Shion's cooking. When he made Gobta eat it instead, just a spoonful nearly killed Gobta and gave him Poison Resistance for surviving the ordeal. Being fed Shion's cooking even became an official punishment in Tempest (much to her ire).
Rimuru: Don't tell me that this is going to be that overused trope where the seemingly-skilled hot woman turns out to suck at cooking! Shion: *brings out the food, and it is purple, oozing, and emanating an evil miasma* Rimuru: Why, trope, why?!
Some special emphasis has to be put on just how lethal this stuff is. In the OVAs, one of Shion's dishes starts melting through the metal pot she prepared it in and burns a hole through the ground, and the "rice ball" she tries to offer Rimuru is so toxic it seems to be alive and fully in pain, and when it ends up falling into the lake, even its water-diffused form is able to poison and make the giant monster within the lake go completely berserk as it lashes out in pain. In the Slime Diaries a cup of "tea" she makes accidentially drops on his slime body, and then it starts melting his body while forcing him to regenerate and trigger both Pain Nullification and Ailment Nullification to keep it from sending him into agony. It's up to the point that in order to make her food safe, let alone edible, for comsumption she had to die and come back to life with a skill that turns her into a Reality Warper. Even then, that only fixed the foods' taste, and it all still looks like some banquet of the damned.
In To Love-Ru, Lala's alien cooking almost killed Rito the first time he tries it.
Misato Gori, a minor character from the original series. The donuts she makes are not only burnt and filled with pieces of egg-shell, they give everyone that eats them food poisoning. She mistakes their tears of pain for Tears of Joy, and believes her cooking is unusual-looking but "cute". Apparently, while cooking, she also burns the kitchen ceiling....
While Yoriko is probably actually a very good cook, she serves as this trope to her friend Touka. As a ghoul all human food tastes disgusting to her and makes her sick if she doesn't throw it up before digesting it, but she forces herself to eat it to maintain her cover and because it's a present from her friend. She even feels obligated to do this when Yoriko isn't there to see.
Saiko Yonebayashi, in the sequel, is also apparently unable to cook. She describes it as kind of like Okonomiyaki, but the results of her cooking are censored and no one is willing to try the results.
Yuka Nitta from Touch. After taking Minami's place as team manager, Yuka's cooking is like this, due to being too exotic. she eventually tones it down.
A few chapters later on in the manga it turns out that her Archenemy, Fujiwara no Mokou, is one as well. The food she prepared also contained mushrooms and, according to Mokou, she thought she was going to die from eating them... only to immediately correct herself and admit that she actuallydiddie from eating them, making her a literal example of this trope. Her guests were not exactly thrilled when she, a couple of minutes later, served them mushroom soup.
Chapter 45 of Wild and Horned Hermit: Shion Yorigami, as a poverty god, has low standards when it comes to food, as shown by her and Tenshi's "Heavenly Banquet". While she gushes over the random weeds they're serving to the point of thanking them, most of the guests are too sickened by them to come back for the next day's banquet.
Twin Princess of Wonder Planet: Twin princesses Fine and Rein. For example, they made croquettes to find a thief. It made a bunch of birds , including the one who stole Altezza's necklace, sick. Only once does their food not get a negative reaction. When they try to awaken a sleeping giant; he ends up enjoying their food.
In a surprisingly cute side-story of Umineko: When They Cry, we discover that there's a reason Beatrice has Ronove do the cooking.
Half a day was spent in spectacular violence that would have shocked the culinary world.
Until Death Do Us Part, justified use of the "looks awful, tastes awesome" variant: the cook in question (Mamoru) is blind, so he can't exactly see how his food looks.
Lum in Urusei Yatsura. There's nothing technically wrong with her cooking, it's just that she tends to overuse the spices to make it taste like the food on her home planet (and by alien standards, she's actually a Supreme Chef). She comments that earth made food is completely flavorless and enjoys drinking Tabasco sauce straight out of the bottle. Also, candy from her home planet causes earth creatures to grow into giant monsters and she forbids Ten from giving it to earth creatures (a warning which he ignores). Despite all her observations she manages to remain oblivious to the issue, probably due to rule of funny. It should also be noted that once, in the manga, Lum's attempts at cooking on Earth opened a portal in the Moroboshi kitchen, from which miniature space fleets erupt and begin to do battle. And once, in the OVA, Ataru is turned into a werewolf by her food.
The title character of Video Girl Ai, Ai Amano, is designed to be an excellent cook... but her faulty incarnation, among its many other defects, is incapable of producing edible food. Still, Youta eats it out of affection for her.
Sumika: "...What kind of food explodes when cooked, and who invented it?" Miyako: "...You did."
Elsie, from The World God Only Knows, prides herself on her cooking skills. Unfortunately, she's a demon from the Underworld, and her idea of good cooking involves such ingredients as eyes, hands, and living tentacle creatures. While it may be delicious to demons (Haqua certainly likes it), it typically sends humans running for the toilet instead. Oddly enough, however, her curses make pretty good curry.
Hatsumi (Eve) of Yami to Boushi to Hon no Tabibito is known in her home economics class and beyond for her lethal pancakes. They look perfect, but the taste... Of course, her love-struck adoptive younger sister (and, as it turns out, love interest) Hazuki chokes them down them anyway, correctly interpreting them as an expression of Hatsumi's feelings for her. Lilith is less forgiving, refusing even to touch them and saying that anyone who eats them is incapable of ever feeling happiness again.
Nozomi of Yes! Pretty Cure 5 has this among her impressive number of failings. It seems to be contagious, as when all the girls try to cook together they have a tendency to mainly just produce chaos (and rice you should probably avoid), even though Urara at least can cook perfectly well on her own.
Natsuki from Yoake Mae Yori Ruriiro Na gets the nickname "Carbon Master" because everything she cooks tends to end up looking like charcoal (even a salad). She improves somewhat in Moonlight Cradle.
Played with in Yu-Gi-Oh! GX; Professor Sartyr is, himself, a very good cook, but his deck is constructed with killer cooking in mind, complete with vegetable warrior monsters, spice-based spells and traps that screw with the opponent's monsters, and his key card, a demonic chef by name of "Curry Fiend Roux".