The Taco Bell Mango Fruitista Freeze has to be one of my all-time great disappointments. I love mango, I love mango flavoring, I've used mango-scented candles before...
This thing tasted like they sprayed mango air freshener over a cup full of ice. So, so gross.
I also have issues with McDonald's in general--their food doesn't usually smell like food, it smells like McDonald's. I can tell when somebody in the office got McD for lunch by the smell, although I could never tell you what they got. It's disturbing and weird.