I have a few 'strange/odd' food preferences that might be unpopular:
I dislike:
Ketchup - Just don't care much for it, it adds nothing for me
Mustard - Cannot stand it. it's nasty. Yellow, the all too common variety, is the worst offender.
Lettuce - Mostly water. Once soggy, is nasty. All too common on burgers.
Tomatoes - Slimy. ick. gritty when fresh and the seeds do not help, especially if not fresh.
Pickles - are nasty. Especially common varieties.
Onions - Nasty. They're awful and often lack any good flavor unless cooked and caramelized to an extent. So I hate them raw.
Strawberry - No thanks. The seeds are my worst enemy ever.
Mushrooms - Commonly tastes like I'm chewing on dirt with a soft rubbery texture. Not usually something I enjoy biting into even if its mixed and cooked into something
I Like:
Mayonnaise - I don't understand why anyone would hate this wonderful condiment, unless they regularly eat Miracle Whip which is not mayonnaise. See a comic on The Oatmeal for an explanation of the flavor differences between the two. {Use google-fu and discretion, it's lowbrow humor}
Broccoli, Cauliflower - Delicious, even straight and raw. That's a vegetable.