Here's mine: I was a vegan at the time, and I had got into the habit of making 'pizza' with a toppinng of vegetables, covered with this 'cheese-like' combination of silken tofu and nutritional yeast wizzed together in the blender. It wasn't great - in fact, it was pretty revolting - but it broke up the tedium. (I will add here, as if it needed to be pointed out, that at the time I was cooking for one. Otherwise, I'd never have got away with it.)
Anyway, this tofu-nutritional yeast combo would have been merely a blip in my record of relatively sound food-related judgement, were it not for the fateful day that I went to the farmer's market and returned with a large celeriac. When I got it home, I was wracking my brain for something unusual to do with it, and I hit upon the misguided notion that it would be really delicious to make a kind of celeriac au gratin with the aforementioned tofu/yeast combo as the topping. I spent an hour lovingly slicing the celeriac, braising it (or something) and arranging it in a little pyrex dish. Then I spred the odious combo on top, sprinkled with breadcrumbs and popped it into the oven.
What emerged tasted like drinking rainwater out of a rusty bucket. It was so revolting that I've never been able to eat celeriac again - it's flavour is, for me, indistinguishable from the flavour of nutritional yeast.
Ok, that's mine. I'm not proud, but I feel a little better for having told you. What's yours?