What food have you eaten that you dislike the most?
For me it's onions. They have absolutely no redeeming qualities. They smell bad, taste nasty and have a really terrible texture. There are foods that taste worse (such as jalapenos) but onions top my list as most disliked.
What makes onions particularly bad? It's because the majority of the rest of the world thinks they are wonderful. There's hardly a restaurant I can go to where they don't add onions to everything. Whether it's soup, gravy, omelettes, stew, sandwiches, salad, etc... it will invariably be served with onions.
Imagine if your worst liked food was loved by the rest of the world and every time you ordered a meal the odds were very high that it would contain that food.