What is one food that most people think tastes good but it actually makes you gag? 

Mine is hummus! YUCK

-Pepperoni

-Sausage

-steak

-bacon

-hamburgers

-hotdogs 

-apple pie

-rice

Edit : I just saw Echoos answers and I'm adding cilantro too. I can't count to one :p 

Cornbread

All seafood except for prawns

Reeses peanut butter cups

Curry

Hot raisins

pork in any form, sausages, pure cheese, chili, whole milk, grilled cheese sandwiches, burritos, spicy chips, popsicles

I'd say lima beans, but I don't know anyone who thinks they actually taste good. Most people eat pretty tame stuff.

Try some frog, cooked in coals In the banana leaf it was caught on.  Rattlesnake, escargot, head cheese, and red ants, man, most folks don't know what they're missing. 

I draw the line at "Chitlins"(chitterlings) though, as most sane people do. That's just nasty. 

Avocados, in any shape or form. Yuk city.

I am with Dragonfly about the cornbread.  That stuff is just nasty.  This can be a problem living in the south.

Everyone seems to like eggs but I've never liked them. I think they smell really bad, look gross, and I don't like the taste either. I guess I have to have them in cookies though lol

Vegemite.  I know I should like it, but I just can't.

Mushrooms!

Seafood. I just don't like it.

Any form of Pizza which has any form of ingredients from the sea. Shrimps, Fish, etc.

Caviar!  You may have my portion of the expensive stuff.

Dehydrated fruit