I once decided to eat some leftover chili. I grated a half-onion into the chili. Grated onion!!! Good God, my eyes started to watrer…:o 
I use Bisquick to make biscuits, but add cheese and red pepper flakes which I’ve ground to a powder. I ran out of red pepper flakes and used tobasco instead.
I have no idea what happened there; apparently tobasco reacts to the milk or something. Ended up with something resembling hockey pucks.
I don’t want to sound like I’m bragging, but I’m a good cook (now!) - it took me a while to come up with a story for this. However, the occasional disaster will usually result in pizza delivery for me as well, because I’m too frustrated to even think of making anything else.
The one that springs to mind is a recent attempt at making a curried dish for my husband. I was chopping a spice paste with a hand-cranked chopper - think large enclosed plastic cup with a handle, and a lid on it with a crank on the top and a chopping blade on the bottom. My sister-in-law had bought it for me for one Christmas, and I’d found it pretty handy. Except for this time - the handle was, for some reason, detachable. It detached while I was cranking it to chop the food, and flew out of my hands. The cup opened up and spilled a dark mix of curry, onions, and tomatoes down my beige pants and onto the linoleum. I calmly placed the mess into the sink, grabbed paper towels and mucked up the worst of the mess, and carefully tiptoed towards the bedroom to avoid dripping anything onto the light-colored carpeting. My husband saw me, asked what happened. I responded, “Get me the phone and the delivery menu; the curry paste threw up on me so we’re having pizza.” He was kind enough to wait until I was out of sight before laughing.
(Some encouragement for folks learning how to cook - I didn’t cook until I moved into an apartment in college, and from there I just kind of took off. These days I have about 40 cookbooks (and yes, I’ve used recipes from all of them), and not only my husband but my inlaws rave about my cooking. Reading the recipes carefully is very important, and find a decent cookbook that bothers to explain how various techniques are done - Julia Child, Jacques Pepin, and Jamie Oliver are a few of the good ones that come to mind.)
My banana bread story is a little different. I too, had overripe bananas that needed to be used. So I measured carefully, had it all perfect, poured the batter into the disposable foil pans I’d bought (since I rarely use them, this ends up being cheaper) and let it start cooking.
Needless to say, don’t use self-rising flour and baking soda (that’s the one that makes it rise, right? Or is that baking powder?). Smoke was billowing out of my oven from the spillage. I opened all the windows in the apartment, turned on the exhaust fan and the fan that was part of the heating/cooling system and still set off the smoke detector when I managed to get the pan out of the oven so I could carry it out to the patio to cool.
My personal meatloaf disaster story: When I was in college, I decided I wanted meatloaf for dinner one night, but I didn’t have any breadcrumbs. So I used crushed cornflakes instead. It was disgusting. Words cannot describe how nasty it was. I never did that again. I make very nice meatloaves now.
Not my fault, but in my kitchen:
Had a few people over for a cookout.
The burgers were done and brought inside to be placed in the microwave with cheese to melt them and keep the burgers warm until the other stuff was ready. So the guy in charge of cheese puts it on the burgers and puts them in the microwave to melt them.
Except the cheese was in those single plastic wrapped slices and he didn’t take the plastic off.
Plus he wrongly put the temp on MED-HIGH and arc welds the plastic and cheese to the burger!
We told him he made tank armor.
I’ll start with a couple of things I saw my friends do, and finish up with a blunder of my own:
A friend’s first attempt at making blackened catfish led him to realize why restaurants that serve it have those enormous vent hoods over the burners. He pepper-gassed the entire household, and we had to wait on the sidewalk across the street for the fumes to clear enough to re-enter the house.
Another friend, known for his ability to make boiled rice that you could cut into little cubes and dip into gravy, undertook to bake some (pre-made) rolls one evening. Other matters distracted him. The next evening after class, he opened the oven to put in some garlic bread and found out what rolls that have been baked for 24 hours look like. He kept one of the little charcoal delights on the window sill for a year as a reminder.
My mistake came the first time I used habanero in a dish. I was making jambalaya for a party, and since all my friends loved spicy food, I decided to try this new kind of pepper I’d heard about. I thought the little warning labels were funny ("Use gloves. Don’t put your hands anywhere near your eyes for three weeks. Biohazard…). Well, a 3-gallon pot of jambalaya takes a lot of seasoning, so I crushed several dried habaneros and sprinkled the flakes. A few seconds later, my fingers were burning and my eyes were watering; I had to turn off the burner and run out of the kitchen. Once I got all the windows open and the fans running, things got better, and I stubbornly finished cooking the stuff (along with an improvised second dish for those who couldnt’ take it). It all got eaten, although we did go through a truly astounding amount of alcohol that night to wash it down…and there were screams the next morning.
Some Dopers with old-fashioned cookbooks or ancient kitchen appliances may understand this one.
When my Mom remarried in 1962, my stepfather brought a bunch of things into the house, including a Fannie Farmer cookbok, which I figured had been published and printed around 1907. A few years later I decided to try my hand at making pancakes from scratch, from this cookbook.
Keep in mind that when this book was published, the most common kind of kitchen stove was the cast-iron wood-burning stove. Here I was, in 1966, using a built-in stove top and a large black cast-iron skillet to make the panckaes. The nearly sixty years of difference showed immediately. The pancakes were not browned, and they had nearly the consistency of a big, flat rubber bathtub stopper, but were not quite so delicate in flavor. I never tried to cook anything from scratch again.