The waffle at CRT a few years ago. My girlfriends breakfast plate came with one and I made a comment with our waiter there about how it wasn't fair that she got one and I didn't. He told me be glad I didn't because they are awful. My girlfriend decided not to have it and gave it to me. I was still trying to chew it a few minutes later when our waiter walked by. It was like wet concreat that began to solidify in my mouth. He laughed at me for trying it (all in good fun, of course). I noticed shortly after we came home that they changed that breakfast menu.
A close second would be most of the dinner meal at 'Ohana. The wings were either soggy or way too dry, the noodles taste like something out of the freezer, the meats were all so dry that not even the sauces could help. The dessert and shrimp were alright, the rest of the meal was just awful.