Well, licorice is definitely up there.

There’s some pralines that with some alcohol based filling that’s also really gross.

But I still remember I was a kid and my parents bought these cheese crackers. They were awful, the it was a bit crumbly but they had this really bad taste of something I can only describe as for fungus & cream cheese. I literally had to take a break and concentrate on not barfing even though we just wanted to play tabletop games. I know it’s not sweet but that stuff lives rent-free in my head to this day.