When this week's topic came up, I knew the answer immediately!
Mussels. By far the most disgusting thing I have ever eaten! I can't stand the taste and especially the texture. My family and friends can devour them in minutes and I am completely grossed out by them. I tried to eat them once at a restaurant while out with some family and I swear I nearly vomited at the table. Blech! So gross.
Following closely are mushrooms of any type. It's a texture thing. Although, I do like mushroom sauce.