I thought of a good one for worst disaster. About a year or two ago I decided to make some high end slow cooker fajitas. I had a beautiful, perfect slab of meat. Was way too expensive, and I bought it on a splurge. I had fresh grown bell peppers and everything. So I sear the meat perfectly, get everything setup in the slow cooker... Meat, onions, peppers (hot and sweet), seasonings, and some lime. This thing cooks for like 12 hours. I test the tenderness, and it is just... jesus, it just falls apart perfectly. But... something smelled off. I tried to put that aside, and go to taste it. ... I've never spit something out so quickly. It was what I imagine athelete's foot soaked in balsamic vinegar and evil distilled into a liquid form must taste like. (A taste I never wished to imagine.) My sister and step brother eat everything I make, even if I don't like how it turned out, and tell me it's amazing and seem to mean it even while I'm finding every flaw. Which I do a lot (I'm very self critical of my food), so they don't really believe me how bad it is. So they each try it. And yeah, they both say "Okay, this time you're right, this is awful."
I start trying to figure out what went wrong, and then someone points out the half of a lime left over smells a little odd. I take a slight taste... yep. That's the flavor. The awful, soul crushing flavor. That soaked into the expensive cut of meat for 12 hours. I go and test the rest of the bag... every last one is the same way. I've never seen anything like it. It wasn't that they were rotten, or over or under ripe, or anything. They were just fundamentally wrong. So about 15 cents of lime juice destroyed what was to be a masterpiece.