Bagels and lox. Sushi has seemed to steadily grown in popularity here in the states but there's still plenty of aversion to raw (or cured, brined/smoked) fish. Also capers are like angry little olives on steroids. Definitely not for everyone. I haven't had any since the only bagel shop around, an Einstein Bros, closed some years ago.

I loved greens as a kid and still do. Stewed spinach, Brussels, broccoli, etc. Seems like it's usually a visual and/or texture aversion for the folks that don't like stewed greens (spinach, collared, kale). Does kinda look like a chunk of dark, wet grass left behind a lawnmower.

Dutch licorice. I haven't been brave enough to try Swedish Bastards but I have to make a conscious effort not to eat a whole bag of Gustaf's dubbelzout coins. I told the person that introduced me to them that they taste the way a litterbox smells... then they grew on me and I kept eating them.

Fresh hot mustard. A local Chinese restaurant makes theirs fresh and it's damned potent. It honestly reminds me of nail polish remover. I haven't found anything that'll clear my sinuses the way it can.