The tough question is food that's prepared well but that you still don't like. I've had bad food before, but most that comes to mind was prepared poorly. Even Brussels sprouts can be truly delicious when prepared well.
The only thing I can think of is
beets. Yes beets, those red root vegetables that are a bit grainy and have a distinct sweet flavor. I've had beets cooked by very talented chefs that I just couldn't get through. I've even had beets with savory flavors like pork and it didn't work. I'm just not built to enjoy beets.
Sorry, guys. It's nothing personal.