Tartar sauce. I’m sorry, but mayonnaise and pickles never, EVER go together.
Cantelope/mussmelon/honeydew melons – actually, pretty much any melon apart from watermelon is foul.
Cooked cauliflower. Ugh.
Whatever flavor they use for Pepto-Bismol. It’s some sort of mint, I know that. Not one of the good kinds, though.
The only thing I truly gag at is raw green peppers. Something about the smell of them makes me have to step away and gulp for air. I almost start gagging walking past the pile at the grocery store, but when I’m cutting one up for chili or something is when I really have problems. Red peppers don’t bother me so much, as they’re not as pungent, and cooked peppers (such as fajitas, etc) I don’t have a problem with much. (I don’t eat them, but having them on my plate doesn’t send me into heaves.)
I don’t like seafood of any kind either…not to the point that it makes me gag though, I just never had the taste for any of it. (One thing that really horrified me is once I used my Foreman Grill to make my husband a piece of salmon and everything I made in it after that had a fishy taint for quite some time. Fishy grilled cheese, fishy chicken breasts, etc. Yuk!)
Anything with even a hint of mayo. In another thread I think I described it as Satan’s mucus. I can’t even look at it without feeling ill. I feel just as strongly about mustard – maybe it tastes good, but the smell makes me ill. I’ve started telling people I’m allergic to it because nobody understands how much I HATE HATE HATE $%*# HATE the stuff. I will never have either mustard or mayo in my own fridge, EVER. Gag.
Liver. Just like Zenster, I adore pate, but fried liver makes me just all oogy inside. My mother used to cook it for her dog twice a week (yes, he was a spoiled little puppy), and the smell always made my stomach churn.
Sunny Delight and Cactus Cooler: both I happened to drink right before I came down with stomach flu or food poisoning. The thought of drinking either is utterly disgusting.
Marshmellows. Specifically, Peeps brand marshmellow disgusting concoctions.
I ate too many one Easter as a little girl. I vomited Peeps all over the manicured lawn of a fancy Easter egg hunt we had been invited to.
Now, just looking at Peeps, or any marshmellow for that matter, makes me feel very nauseated.
Gross.
Cherries. I can’t eat cherries. They make me vomit. I love cherry-flavored things, though.
It’s my father’s fault. He forced me to eat a cherry once. Did the same thing with coconut, but I already disliked coconut, so no harm done that time.
Greens. I just can’t eat them veggies, I don’t like their appearance, I don’t like the smell, don’t like the taste.
Celery. I can’t even be in the same room with celery.
If it’s cooked, like in soup, then it’s not quite so bad, but I still prefer to avoid it.
Cantaloupe: YUCK YUCK YUCK
Corn: I’ve tried it several times, but no can do. It’s disgusting.
Pickles: Why does everyone assume I want this nasty things on my burgers? No thank you.
Not a big fan of mayo, but I have no problem with it in sauces or dressings or anything. On a sandwich though, good Lord.
The only food that has actually made me vomit, at least recently, and when I was in good health, assuming proper preparation? Egg nog. I hate that shit. I can see why it often is made with alcohol though: you’d have to be absolutely plastered to even consider it. Or at least I would.
Another vote for liver. Vile.
Any kind of bell peppers – green, red, whatever. I would not only despise them while I was eating them, I would despise them the rest of the day as that horrid taste kept repeating and repeating… I cannot believe the number of things that people sneak them into.
Corn, mayonnaise, cittage cheese egg salad, potato salad, milk, and cream chese are all pretty gross.
I used to gag at the thought of walnuts. Then, a few years ago, I choked down a walnut cookie to be polite. My mouth and tongue swelled up so bad, I was on Benadryl for a week! Turns out I’m quite allergic to them. Oh well, at least I don’t have to be polite about them any more. 
And hard-boiled eggs - Gah! I can hardly cook them for the kids at Easter. Yuck-O!
Oddly enough, I love fried liver.
Watermelon, however, sends me into dry heaves every time I try to convince myself that it can’t be that bad.
I feel muchly the same about cantaloupe, honeydew, etc. Blech blech.
I also get pretty ooged out by raw tomatos… it’s the mucousy-seed part that gets me.
Raw okra has the same effect. shudder
Until recently, I thought there was no food whatsoever that I didn’t like.
Then I tried limburger cheese: barf!
And then I went to Great Britain, and tried haggis, which is made from stuff like sheep entrails and lungs and suet, encased in the sheep’s stomach. I forced myself to swallow one piece, then immediately regretted it.
Heh…almost everything anyone here has said goes on my list!!!
(Did I mention I’m a picky eater?)
laughing. my. ass. OFF @ what Mirror Image egamI rorriM said about onions…god, that is SO true! I’ve often thought maybe it’s not the taste so much as that sickening crunch that causes my entire body to react like I’ve just chomped a great ball of aluminum…but then I unknowingly took a bite of spaghetti with tiny, soft onion slivers and upon tasting them my mouth became paralyzed such that all I could do was open my mouth and let it slide back out…so I guess it’s both. I honestly hate onions to the point that I think I’d rather find half a worm in my apple than half an onion.
Oh, and I absolutely DESPISE devilled(sp?) eggs. How can you eat something that smells like a geriatric fart??
Amen brutha (or sista as the case may be).
Clams and oysters are vile. Mollusk also is not food.
I’ve never tried, but I don’t think I could get tapioca down. Ick.
Also, the smell of cooking leg of lamb (say, in a soup stock) makes me run screaming from the house. :barf:
I’ve eaten and enjoyed many of the things already mentioned here, but I too must draw the line at liver. Gad, it stinks, looks horrible and (probably) tastes even worse.
And I can’t bear the scent of papaya. Vomit, you say? That’s what it smells like to me.
A nutritionist asked me once what my favorite food is. It’s mayonnaise. I could eat it with a spoon.
Least favorite – Brussel sprouts, pork brains, kidneys and liver.
My mom forced me to eat brains mixed up in scrambled eggs when I was a kid.
Does anyone know if foie gras does or doesn’t have that awful liver taste? I noticed that three of you that can hurl liver still like pate.
Ah! But I love f-f-f-f-fava beans. 
Foie gras has a very light liver taste to it, but it’s nothing like beef liver. Plus, pate is a totally different way of preparation than fried liver.