Veronica Lodge. Being the Spoiled BratRich Bitch that she is, don't even suggest that her cooking is anything less than superb. In one comic, Veronica was preparing what Archie called "rainbow cookies". Since they looked like ordinary cookies, Mr. Lodge asked what he meant by that. Archie responded with "Sometimes they make you turn blue, sometimes they make you turn red, sometimes they make you turn green..." Later in the comic, the president of a food company tried her cookies, and the result prompted Archie to say, "Purple? Never seen that color before!"
Another comic shows Reggie eating some dinner Ronnie's cooked for him, but he finds it inedible; so he dumps the whole plateful into the dog's dish, then tells Ronnie that the food was superb. A moment later, the dog sniffs at the food in his dish—and picks up his dish with one paw and empties the whole lot back into Reggie's plate.
Ms. Beazly, the lunch lady. Students who eat at the cafeteria are inevitably shown later doubled over in poisoned agony, and the school staff isn't too fond of her food either. One case of stomach cramps she was blamed for, though, was actually the result of some stickers popular around the Riverdale High students; their glue was toxic enough to cause them. When Archie with Professor Flutesnoot's help proves this one time she was innocent Mr. Weatherbee is quick to reinstate her—and Ms. Beazly gives Archie a gourmet-level meal in thanks!
Olive from The Beano (she's a "School Dinner-lady", who is a Lethal Chef subtype of her own). Her "Tea" was actually a highly-reactive acid-like corrosive; her oxtail soup moos and flicks its tail; the skin on her custard couldn't be broken with a pickaxe, and so on.
During the short time Spider-Man's Aunt May was dating Willie Lumpkin, Peter was seriously turned off by his lasagna. In one story, he took them and Mary Jane to a special art exhibit after eating it, and spent most of the time trying to find a place where he could throw up. (And in the second part of the story the next issue, he implies that he's taking Kristy to the museum simply to avoid having to eat it again.)
In one particularly badly-written issue, Alfred took skill levels in lethal chef. He ran out of baking soda, so he used salt instead.
The Robins from Li'l Gotham arn't much better, if their attempt to cook for Alfred was any indication.
Moira MacTaggert and her coffee. If there was a complaint desk in Excalibur's Muir Island base, probably this would be on the top. To the extent that when Kitty volunteered to take Pete Wisdom to London to check on a friend of his, Brian told him "Buy some coffee while you're there! We've run out of Rory's good stuff." And it didn't even escape Xavier's notice. He once quipped that Jubilee was using Moira's coffee to lubricate her roller skates, and also remarked on it during a video-phone call with Moira:
Moira: Och, it's noon and I'm still barely up. It's the break o' dawn wi' you and ye look fresh as a daisy. Ye make me sick, Charles Xavier.
Professor X: No, Moira. It's your coffee that makes you sick.
Yosefa from the Israeli comic Zbeng! specializes in inedible, rock hard doughnuts. She once used a batch of radioactive yeast to make them extra fluffy, which created a gigantic mutant doughnut that threatened to crush the school.
And even worse, she has a truly loving boyfriend, who eats everything she cooks. He is a model patient in the hospital's stomach pumping section...
He not only tries to mix fish and strawberries with cream and alcohol, he actually manages to make a living sauce, which escapes its bowl to crawl around...
He also invented the "horror kitchen".
And almost assassinated the president with a flambéd crêpe. Apparently, he was using rocket fuel as the flambéing reagent.
In Bone, Gran'ma Ben/Rose's teacher tries to put stinky cheese on Smiley's quiche and serves up some disgusting green stew that practically everyone despises. Bartleby, on the other hand, loves it.
The Cook from Sturmtruppen. His spaghetti is known for strangling soldiers and he once turned the lunch in a living monster. When the Sergeant added motor oil to his soup, nobody noticed the difference until a motorist asked for his oil can back.
Calamity Jane from Lucky Luke. The first time she attempts to cook cookies, she has to threaten her clients with a rifle to convince them to taste them. And even then one of them is willing to die rather than eat.
Monica from Brazilian comic Monica's Gang is prone to cooking awful things such as gumbo flan, yogurt pizza, or a "health juice◊"note in case you're wondering, the characters become dinosaurs because of a serum that fell on the juice, not the juice itself.
Two examples from the comic book version of W.I.T.C.H.:
Will's attempts at cooking includes things like baking with powdered soap in place of flour.
Orube, an alien friend who, when first arrived on Earth, mistook money for food (she complained it didn't taste well) and has apparently set on fire the kitchen the first time she tried to cook. Differently from Will, it's more about lack of familiarity with Earth cooking implements and ingredients (in a later special it's confirmed she never set the kitchen on fire again) and clumsiness when trying to cook for other people (she destroyed the water tap in her kitchen while preparing pasta due being in a hurry), even if she still has a long way to go (in that special she managed to burn the pasta).
Granny from Popeye has somehow managed to burn water and her biscuits have been used to pave driveways. Her cooking is so bad, Popeye, Poopdeck Pappy and Swee'pea only allow her to cook one meal a year, and on that day, they usually sneak out to Roughhouse for a hamburger.
Mortadelo y Filemón: One of the Running Gags associated with Ofelia, with the aggravating factor that she believes herself to be a great cook. Mortadelo and Filemón would often ask for some of her homemade dishes, only to use it as rat poison or to purge their bowels.
The cook from Astérix The Legionary is a subversion. Ordered to cook legionary rations according to legionary standards (flour, bacon and cheese, in one pot to save time), his food is almost inedible (it's implied the Romans deliberately feed their troops bad food to keep them in an angry, combative mood), but given proper ingredients and the motivation to use them, he can work wonders.
A Disney Comics Donald Duck story had Donald trying to barbecue steaks but ending up burning them so badly that his nephews proclaimed them to be as hard as rocks. The final panel showed Donald calling a paving company to cancel his order for flagstone steps because he'd "made other arrangements..."