Oooh, you just reminded me of a place. It was/is a bagel shop, Mrs. Cheesesteak and I stop in to get a couple of bagels, and it didn’t smell right inside. Just really not right, but I couldn’t put my finger on it. But we ordered the bagels and when the wife asked if I wanted to sit and eat, I said “let’s just eat in the car.” The bagels were fine, though.
I eventually identified the smell, it was like old vomit, not quite cleaned out of the carpet. Never been back, will never go back.
Minimal sauce is pretty normal on Italian style pizzas, but the stale bread part and cold cheese really isn’t. (Though they tend to be pretty sparing on the cheese, as well.) It’s all about the dough and the bread.
I’ve had food poisoning twice from restaurant food, but since it tasted OK going in, that doesn’t fit the criteria.
Recently, I got a brisket sandwich at Arby’s drive-through. It was all fat. Hardly a speck of meat on it. I had to tear it apart to get to any meat at all. The one my wife got was fine. Mine was inedible.
I had a similar experience at a Roy Rogers restaurant years ago. A roast beef sandwich that was just a mass of gristle. Tough as horse meat. Trigger? Where are you?
I’ve had restaurant food that wasn’t particularly good, but at least you could eat it. These two rose to the level of not being able to eat them at all.
I went to a Japanese Izakaya (small plates) place years ago, and they had a seasonal specialty on the menu: firefly squid. I normally like any and all kinds of fish, from mild to strong-tasting types.
But this stuff tasted like strong, fishy liver. Not good liver, but horribly strong bitter stuff. I couldn’t even raise a second bite to my mouth. It was weird - usually squid is a mild or even flavorless kind of sashimi. But not this stuff. Ick!
Around 1980, I got a pizza in Westfield, Mass. that was topped with Campbell’s tomato soup and Kraft slices.
There is a restaurant about a quarter of a mile from where I live. When I first moved out here, I was getting home around 7 and didn’t have anything handy to eat. So, instead of wrestling with that situation, I decided to stop at this place for dinner. I remember ordering broasted chicken. It was caked with batter, and it was greasy and not crisp. The mixed vegetables looked and tasted like the kind you eat out of a steam bag you buy in the freezer section of the market. I ate the leg, two bites of the vegetables, and the mashed potatoes, which tasted like instant mashed potatoes.
YUCK! 
For a food that’s supposed to be good, even when it’s bad, there’s a surprising amount of pizza in this thread. Here’s mine. Mrs. Charming and Rested picked a pizza restaurant in Saigon. I have no idea why. It looked dirty from the outside, there was no one inside. It made “the best pizza in town!” and was clearly targeting tourists, which is never a good sign. But I went along, because she had picked innumerable great places up to this point. The listed specials were all unappetizing, like cha lua (Vietnamese sausage) with mayonnaise and lychee or other seemingly inedible combinations. I picked a couple of toppings a la carte and hoped for the best. My wife just asked for a bowl of pho, which I’m not even sure was on the menu.
Everything about the pizza was wrong. The crust was tasteless and tough. The tomato sauce was sour, maybe with vinegar or fish sauce and otherwise lacked any spices. I could not recognize the cheese but it was vile. I don’t remember what toppings I chose but they too were disappointing. Still, I picked them off to get something into my belly. When she saw my food, she asked, “why did you get pizza in Saigon?” I asked, “why did you pick an empty pizza place?”
I went to a fancy restaurant that specialized in using all the parts of the pig for various pork dishes. Everything was over salted. The mushroom appetizer wilted under the salt. The mashed potatoes tasted like soggy potato chips with extra salt. I got creamed spinach with enough salt to clear an avalanche. The braised pork had enough sodium to restore the Bonneville salt flats. It’s too bad because the flavors were all solid. We never ate there again and it closed a while later.
Was on holiday in Bulgaria back in 2013, ate at a big restaurant in an Eastern town on the coast. Asked for Greek salad, chips (fries) and extra sliced aubergine (eggplant). First the sliced aubergine turned up. They waited for me to eat it before taking the plate away. Ten minutes later the chips turned up, all alone on a big plate. Five minutes after I ate them they took the plate away and I waited for my Greek salad. Three simple things I wanted on a plate together all served separately over the best part of an hour. It was so funny, my companion, who got their food all at once as they ordered a set meal, was in hysterics.
Timely thread because the worst restaurant food I’ve ever had was just last week at a little taqueria in Salem. Well, it called itself a taqueria but it was a sit-down restaurant. I ordered some grilled chicken which wasn’t too bad except for the cucumber kimchi that came with it. That was pretty bad
However, I was dining with family and my uncle ordered a big plate of squid ink pasta. Big enough to share. Not wanting to be rude I took a small serving. It looked gross and tasted worse. Like vinegar and cat shit. It took every ounce of willpower I had to swallow the spoonful I had taken. It will be a damn long time before I again eat anything black.
Before last week I would’ve said the worst “food” I had at a restaurant was a cup of coffee at a Denny’s in Pendleton maybe a decade ago. I just tasted rank. I don’t know what rancid is supposed to taste like so maybe this was it, or maybe the coffee pots had never been cleaned, but whatever it was, the coffee was vile.
Recently in Paris, I made the mistake of ordering Andouillette, thinking it was the French version of Andouille. It is not. It’s a sausage of chopped pork large intestines stuffed inside a whole large intestine. As I said in another thread, it’s like standing in a cow barn while chewing rubber bands with a delightful mustard sauce.
For consistently bad, the winner is Panda Express. I don’t think I’ve ever had anything from any location of theirs that rises above “pathetically bad.”
The worst individual dish I remember being served was haggis. Took a bite under duress from my mother and traveling companions. I eventually forgave my mother.
Scary thought: Maybe it actually WAS “the best pizza in town”. 
Years ago, I lived in a tiny town on the Highline (US Highway 2) in Montana. A Chinese family had settled there, and, as you do, they opened a Chinese restaurant. It was very good. We were lucky to have it and them in our community. They became personal friends.
The owner invited us for a special, private meal where he would serve the best and most authentic Chinese dishes. What a treat! The food was superb.
Unfortunately, he also hauled out what he told us was some very fine authentic Chinese wine – and that was undrinkable. The bouquet was like getting a snootful of whatever a bad mortician drains from a half-decomposed body, trying to salvage that which cannot be salvaged. The taste was correspondingly awful. Each time our host left to retrieve another food course, we dumped our wine into plants tastefully surrounded our table. How the plants lived, I’ll never know.
If it’s food you want to hear about, I’d have to nominate the small diner in a whistle stop near where I currently live. The village doesn’t have a post office. It consists of the diner, a tiny gas station with a private convenience store and auto repair shop. The diner itself seats maybe 25 people, including the seats at the counter. Counter seating affords the customer a clear view of the grill to watch their food being prepared. Sometimes this is a feature. Sometimes a bug.
The diner has had many owners and iterations. In one of them, diners were treated to the sight of their cook preparing their food with a .45 strapped to his hip. Not really a welcoming vibe.
I ordered scrambled eggs and toast. I think he used the eggs to clean his grill and the toast to give it a final, thorough scrub before sending out my meal. At least, that’s how it tasted. Couple of bites, I was out of there. They closed 2 weeks later and the place hasn’t found a new owner since.
Had some Carbonara at an “Italian” restaurant. The pasta was crunchy. Like un-cooked levels of crunchitude.
I think that a substantial part of ‘worst thing’ you’ve ever eaten includes expectations vs results. Yeah, I’ve had terrible, terrible food at Denny’s at 1 am in the middle of a long drive, but my expectations for Denny’s at 1am are so low that it isn’t worst, it’s just terrible as expected.
I think overall the worst food I ever ate was at El Arroyo in Austin TX, keeping the above in mind. We were in town to be with friends for New Years, as we try to be most years. I grew up in southern NM, so I have strong opinions on what I consider ‘good’ Mexican or even Tex-Mex food, but figured a local icon in Texas couldn’t screw it up too badly. My wife was craaaaving Mexican, and my local friend said that the food was fine, just overhyped, and so we caved to my wife’s cravings.
I’ll leave out the non-food issues, such as the dirty tables, the utterly uncaring staff, the unspeakable slowness, and the rest of the reasons to NOT go there, and concentrate on the food. Which, was, terrible. Possibly due to the staff / slowness issue, my relleno plate arrived at the table cold. And by cold, I mean it looks like the whole plate had been sitting in the fridge all day, and they had thrown in a microwave for 2-3 minutes to get the surface barely warm.
I choked down the rellenos, which were pathetic, with the inner cheese still cold, and the batter a soggy mess because I was hungry. I couldn’t make myself eat the cold refritos on the side, because I could see the grease slick form from the minimal reheating, and after my immediate hunger was assuaged, I wasn’t that desperate. Honestly, the food was so cold that I couldn’t fully evaluate the taste, but overall it was like something you bought at a truck stop, threw in the microwave and nuked, which again, is my full expectation of what they had done.
All else being equal though, I had the BEST experience of the three of us who ate there that day. Because my wife and friend were down with food poisoning for the rest of our trip after eating there.
I recently ate in a self-styled Irish pub in Wisconsin. I ordered an Irish boxty, a dish normally made with mashed and grated potatoes. This version added pulled pork (or beef, not certain) and left out the grated spuds. Basically a glob of mashed potatoes, a layer of meat, another glob of mashed potatoes, fried, flipped and fried. Doesn’t sound bad, but it was crap. I’ve had worse things served to me, but not in a restaurant; well, maybe at a Denny’s.
a long time ago I used to stop at a coffeeshop on the ground floor of my training facility for my morning container of iced tea. It was usually fine tasting but on that morning after they filled my Cup from the spigot of the tank and while waiting to pay I took a drink. there was something gelatinous in my drink. I spit it out on their counter and left told them it was really REALLY bad spoiled tea. left and never went back.
I once got a bowl of Bun Bo Hue at a Vietnamese Pho place, thinking that if pho is as delicious as it is, then maybe some of the other soups might be equally great. Supposedly according to the Internet, it’s a “hidden gem” and some kind of amazingly awesome dish.
I was so wrong.
The bowl I got had broth that tasted vaguely of beef, but was kind of musty and funky in a way that reminds one of dirty dishwater, and the bowl was festooned with all sorts of mystery meats- crunchy gristle, some sort of congealed blood type thing that still showed can-marks on it, etc…
It was godawful. I ended up hardly eating any of it and grabbing a hamburger on the way home.
That doesn’t sound too far off the real thing:
The broth is definitely a bit funky – a mix of pork and beef – and the main flavoring is lemongrass and fermented shrimp paste. I definitely would say it can be a bit unusual for American tastes.
Despite being an eater with definite preferences as to how things should be done, I really can’t conjure up a memory of a truly horrible meal I’ve had. I get irked when I see a green ring around an egg yolk in anything that has hard-boiled eggs in them, but I’ve never had anything I couldn’t eat with at least a mild sense of enjoyment. (Oh, and this includes some eggs that were off in a restaurant in Transylvania. My co-diners warned me, but it seemed “good enough” to me. Enter three or four days of being sick with what I presume was salmonella, but I enjoyed it fine at the time.)
Bun Bo Hue is one of my favorite things to eat and, in my opinion, far superior to Pho. People like what they like but I would describe it as fresher and richer than Pho and without the clove/anis flavors.