For me it's cheese! Any kind of cheese!!!! I am in LOVE with CHEESE!!! Cream cheese, cheddar cheese, brie, mozzarella, provolone, you get the idea! 
However, I have a friend tell me that she thought it was disgusting!
even though she relished ketchup sandwiches! Blergh!
I knew another guy who could simply eat a raw onion like an apple, no problem! My autist mind thought, "I wonder if he will be a serial killer one day?" I know, I'm weird! HA!
What one food do you enjoy tremendously on it's own, but according to some people, it makes them want to gag?