Raw celery. Most people seem to say it has no flavour. To me it smells and tastes similar to vodka and makes me sick to even think about. It's also kinda squeaky on the teeth which is unacceptable. Cooked in a soup or whatever is fine.
Cabbage rolls. Specifically that combination of ingredients has made me sick by smelling it in the past, though it's not as bad now as an adult, and they do taste good. Cooked/boiled cabbage in any other context never bothered me.
Pickled onions. I love onions and can eat them raw, but I couldn't even finish one mini pickled one due to the resemblance to stomach acid, taste and smell.
Yup, it can add some nice colour, but besides that there isn't much point. Thanks for the celery validation.