Eggplant and okra, although I have found one preparation for both of these icky items that I actually liked. The eggplant was in an Indian curry dish called bharta and the okra dish was flash fried (so it wasn’t slimy) and it was dusted in teff flour (at an African restaurant).
It’s funny, all of the vegetable items that everybody else listed, are what I live on. I have a particular fondness for sauerkraut.
When I was a little kid, I hated most of these things, but when I grew up and knew that I was going to be a vegetarian, I learned to not only like, but love most of these things. I read somewhere that it often takes 10 to 20 tries at tasting something to acquire a taste for new items. I was lucky, I found people who knew how to cook really well and the formerly yucky items took on a new life for me.
When I was a young’un I ate hardly any meat, and virtually no seafood (save for tuna fish sandwiches) so it was an easy transition to becoming a vegetarian. At the time, I was unfamiliar with a lot of vegetables, but I quickly changed that fact and it opened up a whole new world for me.
I remember tasting brussels sprouts for the first time at a Christmas party and thinking they might just be the best vegetable in the whole world. It was similar to This Recipe only without the bacon.