Onions. And just to make matters worse, they are just the perfect ingredient for EVERYTHING. I really...really hate onions. I will pick onion out of a dish if I have to. I don't care if it's Christmas.
(I'm kidding I'd probably eat it at Christmas...but any other day nawww, f*** onions.)
And baked beans, along with many other beans. And also most soups, and...natto and umeboshi. Those being deliberately rotten beans and pickled plums, both from Japan (even in Japan they are polarising foods, bit like Vegemite for Australia). To my credit, I tried them before vowing never to eat them again. I didn't have a problem with fish stomach, so I'm allowed to dislike a few things.