Poutine - By request at KFC's in French-speaking Canada.
As an occasional viewer of the Travel Channel's Man v. Food, and as a person who tries to avoid extreme eating situations whenever the opportunity for one presents -- that is, I TRY -- I've been fascinated with, well, food that is bad for you. And the larger the amount, the better. All this is to say that one of the prime places to find interesting and unhealthy food are the usual fast food restaurants. I've been hearing for years about the "secret menus" at one place or another -- In-n-Out Burger on the west coast, usually -- but apparently these "insider specialties" are catching on. Whether it's the Wet Fries at Arby's, the Poutine at KFC, the Pie McFlurry at McDonald's, or the London Fog at Starbuck's, I vow one day to have given all of these a try. Coupon Sherpa has a post from earlier in the year with one of the best lists I've found of secret menu items.