Well, I’m going to focus strictly on the ‘common’ aspect here, 'cause there are a lot of weirder foods I’ve never eaten.
Until I got to college, I had never eaten:
Sugared breakfast cereals
Twinkies et al
Those weird semi-cheeses (cheese food products, I think they’re called)
Spam
Kool-Aid
Cup o’ Noodles
Circus Peanuts
Funnel cake
McDonald’s (Burger King, et al) hamburgers
Cheetos, Fritos, etc.
Cocktail weiners, or whatever it is you call those canned little hotdog-like things
etc.
I think you get the general idea. After my college friends discovered the lack, they tried to get me a little more in tune with American Food Culture. I ate:
Sugared breakfast cereals - not bad at all. At least, some of ‘em weren’t. Corn Pops and Honey Smacks (or whatever they’re called) were pretty awful, though.
Semi-cheeses - never, never again. They taste exactly like what you’d imagine cheese vomit would taste like.
Kool-Aid - bleh. If I want to drink overly sweet and weird-colored water, I’ll just dump a whole bunch of table sugar in, add some food colorings, and cut out the middle man, thanks.
Cup o’ Noodles - well, it was college. Need I say more?
Cheetos, Fritos, etc. - I ate 'em. Won’t be going out of my way to eat 'em again.
Twinkies, Spam, McDonald’s hamburgers, and other assorted scary food items will continue to be forever untasted by me, since they aren’t vegetarian. (Note to omnivores: talk about your compelling reasons to be vegetarian.) Circus Peanuts will remain forever untasted by me because a) they aren’t vegetarian and b) even if they were, I’d still rather throw up unaided. The smell alone is bad enough.
I still wonder about funnel cake, though.
Oh, and zev_steinhardt reminds me of one staple much touted by my more orthodox family members that I refuse to eat, both on general and specific grounds: tongue. Ew, ew, ew, ew, ew, ew. Can’t say it often enough. My aversion to this, as well as to other organs, goes well beyond general vegetarianism; I could be entirely carnivorous and I’d still refuse this stuff.