In Love Roma Negi cannot cook to save her life, even her boyfriend claims her cooking brings back bad memories.
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.
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.
The super ditz in Girls Saurus DX said that when cooking she could mix up sugar and potassium cyanide!
Akane Tendo in Ranma ˝. Starts out horrible and slowly learns how to cook certain dishes such as curry and tofu acceptably (but still generally very bad tasting results) from her older sister Kasumi over the course of the manga. Ranma ½fanfiction, however, has created a body of fanon that attributes far more outrageous results to her efforts.
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.
Shortly into the last third of the manga series, Akane is capable of cooking 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 the anime, at least, Akane actually straddles the border between this and Cordon Bleugh Chef; while she does get distracted, not pay attention to what ingredients she's using, and generally acts much like a Lethal Chef, she doesn't help her case by the fact she often actually intends to make her own "unique" concoctions when she's cooking, ignoring the real recipe for one of her own devising. And refusing to taste her own cooking can't help...
Fanfic exaggerations of Akane's kitchen incompetence can be wonderful sources of comedy. "It wasn't trying to molest you! It was just being friendly, OKAY?!"
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, The Curse of the Red Cat Gang, Akane's cookies and lunches are items which cause one or all enemies, respectively, to be instantly defeated.
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.
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.
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.
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 B.S.O.D. 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.
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.
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...).
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.
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.
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).
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.
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.
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.
Variation: Ren, in a cooking contest in DearS, causes humans' eyes to bleed... but the other DearS love it.
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.
In the Cooking Duel in Mai 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.
Arika in the (subverted) Beach Episode in Mai-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.
Taken Up to Eleven in Cinderella Monogatari 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.)
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.
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.
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.
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.
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.
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.
Bianchi from Katekyo Hitman Reborn! 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.
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.
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.
In Cardcaptor Sakura, Chinese Girl 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.
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.
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.
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.
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.
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.
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.
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 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.
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.
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).
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.
Tsukamoto Tenma and Sawachika Eri from School Rumble qualify. Their rice balls led to ... bad things.
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.
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.
The flying pie monster from the Kirbyanime produces pies that not even Kirby can eat.
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.
England from Axis Powers Hetalia 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.
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.
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.
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...
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."
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.
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.
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".
Miyabi of Ninin Ga Shinobuden. 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.
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...
The boss of the Gaba thieves in Doki Doki Densetsu Mahoujin 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.
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.
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.
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 Pilaff. In an interesting subversion, the manga's English language eManga/ditor made Grapefruit Pilaff herself, thought it was nice, and published the recipe.
Lead Onidere character Saya's cooking is so lethal that her fellow gangmembers 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.
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.
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."
Misty had also tried her hand at cooking when Brock was sick. It wasn't pretty.
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.
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.
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.
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.
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?
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.
Himeji Mizuki in Baka and Test: Summon the Beasts. Yoshii has violent hallucinations of being dragged off by grim reapers just by smelling it. And when he actually has to eat it... It's explained later that this is because she uses a lethal poison as a preservative. Oddly enough, her food looks beautiful.
Fushigiboshi No Futago Hime: 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.
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.
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).
Sakura Haruno from Naruto in the anime once made a strength potion, but we don't know if it was any good. No one ever was able to put it down their throat (Except Naruto, when he was doing some VERY important training. Though he probably would have eaten it anyway since Sakura was the one that made it).
A variation occurs in Love Hina. Naru's cooking consistently looks inedible, but just as consistently tastes good.
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.
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.
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.
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.
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.
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.
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".
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.
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.
In To Love-Ru F, Lala's alien cooking almost killed Rito the first time he tries it.
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.
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.
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 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.
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 never works out for him.
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.
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.
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 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.
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 uninteresting. Miia, however, is firmly in lethal chef territory, with a bad habit of cooking fish skeletons into every dish. 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.
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.
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.
While in the library in episode 4 of Koufuku 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.
During the curry-making contest in Kantai Collection, 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.
Exploited by Isami in Kiniro Mosaic, when she claims her best dish is fried eggs, burnt to a crisp, to get out of helping the girls with baking.
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 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.
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.
Subverted beautifully by NaoSadatsuka from Shokugeki no Soma. 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.
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
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?
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.
Luffy wastes a whole week worth of food supplies into a giant, uneadible soup of rotten food, putting him and his friends into 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.
Kuroko no Basuke: Riko Aida's food is so bad, people pass out after eating it a couple of minutes later.