Watermelon. I hated it as a kid. Then in my early 20s I attended a weeklong retreat in an isolated area (no car, no transport, no leaving the property) and the only fruit served was watermelon. I thought I might as well try it and after a couple of days found that it was edible after all.
Lima beans. I discovered the small baby Lima beans are very tasty.
Broccoli. It’s good with cheese sauce. Restaurants often serve, over steamed and soggy broccoli. I think that’s why it gets a bad name.
I’ve still never acquired a taste for squash.
Bell peppers. I can distinguish very little difference between red, yellow, or green, and they all have an almost overwhelmingly bitter flavor, and the smell is just the same as the taste. Growing up, my father bit into them like an apple, insisted they were sweet, and I almost gagged at the idea.
As an adult with a significantly more advanced palate, they are one of my last hurdles in my self-training to eat vegetables. They still taste bad to me, but I eat them anyway. I no longer gag at the taste, and they are better cooked than raw (the softer the better) and I no longer cringe at the idea of them.
I had the same issue becoming an adult and drinking black coffee and beer. Both which I feel taste terrible (bolder and hoppier are the worst, respectively) but I can drink them in better than moderate amounts if I have to.
It seems as though many of the people in this thread are posting examples of foods that they once despised, yet now love. Well, I don’t love vegetables, but I do now eat vegetables, where I once despised them. I came to find out that I just didn’t like the way my mom cooks vegetables, because her preferred method of cooking vegetables is to boil the taste out of them.
I found this particularly jarring, in light of the fact that she was a country girl, who grew up on fresh vegetables: she actually prefers them canned, and overcooked.
Sauerkraut.
As a child, I wouldn’t touch it, as it smelled like farts and looked gross, and was something my parents ate with gusto, which made it somewhat immediately suspect. Plus, the “Krauts” were the bad guys in a lot of those old war movies I watched as a kid.
Got to college, had a roommate who when we were discussing what to eat while watching a football game with some friends, he suggested brats and sauerkraut. Not wanting to look like a wimp in front of my buddies and a girl I was interested in, I just sort of decided that no matter how nasty, I’d go ahead and eat it. Shockingly, I discovered that I really liked it, even though it does smell like farts.
Almost any vegetable can be made delicious by the Maillard reaction, aka browning.
Me too. Despised them until one day mom sauteed some in butter. Awesome!! Why didn’t you think of that a long time ago mom?
Sushi, now I can’t afford the quantity I’d like to eat! Still will I never ever never ever ever touch mayonnaise or liver of any ilk. Not a fan of lentils, except for Daal
Yeah, when I was a kid we only got peas in cans, and canned peas are disgusting. When I got older we moved to a place where we could have a garden, and I found out how wondrously good they can be fresh off the vine. Now I’ll eat frozen peas,but I still won’t eat the canned ones.
Fish - As a kid, I was only served fish sticks or deep-fried fish. I hated fish until I moved to Florida as an adult and discovered the wonder and joy of grilled, saltwater fish. Turns out, I’m not a fan of freshwater fish nor deep-fried things. Or frozen, breaded squares of fish-like food products. However. I’ve always been a huge fan of tuna, especially in tuna casseroles.
Sweet potatoes - Ew. To this day, I can’t understand why some people season sweet potatoes with more sweet. My stepmonster would make them with marshmallows and brown sugar and they’d be so friggin’ cloyingly sweet, I couldn’t stand it. I learned to love them when I stumbled on sweet potato fries/chips at a fair this one time and that’s how I started cooking sweet potatoes with savory seasonings like cayenne pepper, black pepper, and a little salt. YUM.
Spinach - TBH, I still hate canned or frozen spinach. If it’s not fresh greens, I ain’t eating it. But I love a nice crispy spinach salad and have them probably 2-3 days a week. Love fresh spinach.
Beets - See also “sweet potatoes.” I don’t like them pickled and that’s the only way I ever had them – straight out of a can. Then one day I decided to try a new vegetable once a week and picked up some beets. Holy god, roasted with just a little salt and pepper? DELICIOUS.
Mostly this boils down to my parents overcooking veggies and serving canned or frozen stuff rather than fresh.
I’m still not a fan of any melons, most squashes (I’ll eat a little), raisins, coconut, and lima beans.
Apples. Thanks to the dominance of Red Delicious apples when I was growing up, I could never understand why anyone liked apples.
And I still don’t understand why anyone likes Red Delicous apples. Every one I’ve ever had has been mushy in texture, and with little to recommend its flavor.
But over the past couple of decades, a much wider variety of apples has become generally available, and most of them are crunchy, juicy, and quite tasty. I usually slice up an apple in the morning, take it to work in a zippie, and munch on slices when I get hungry away from lunchtime.
Spinach. Mom made us eat canned growing up, barf. Cooked fresh in a pan, though, with a little butter and garlic…I can gorge myself to bursting on it.
Funny, I was raised in the 60’s by a Depression-era great-grandmother, and I grew up hating everything. She was a terrible cook. It’s surprising I didn’t stave to death.
As a child, I hated vegetables, all vegetables. It turns out I really only hate canned vegetables, and frozen vegetables that have been boiled to death. As an adult, I like most vegetables, either raw or fresh and properly cooked (except cauliflower, beets and Brussels sprouts, those are still disgusting).
Just wrap it in bacon (if you eat bacon, that is.)
Get thicker asparagus, and cook till the bacon is done. 
When I was a child, asparagus was a grayish-green ‘vegetable’ that had been boiled long enough for it to become limp and slimy; my parents then smothered it with enough mayonnaise to (I assume) completely mask the ‘flavor’, if not the texture.
I was at least well into my twenties when I had a restaurant meal including grilled asparagus. I could hardly believe that the flavorful green stalks on my plate, that I needed to cut with a knife, were actually related to the ‘stuff’ that my mom used to make. Today asparagus is one of our ‘go-to’ vegetables when it’s in season (and occasionally when it’s not).
Sauerkraut, spinach, coffee, asparagus, steak, and cottage cheese are all items I enjoy now but would not touch as a kid.
My grandmother had the foulest, most rancid churn in her kitchen when I was a tot.
All dairy was off the board then and thereafter. I notice the OP only requires “can now eat.” I can now do so, but only in small quantities. The sight of buttermilk still makes me retch.
…then toss the asparagus.
(Just kidding, I love good asparagus.)
Red delicious apples can be pretty good, but you have to get them at an orchard. Their texture and flavor deteriorate far too fast once they’re off the tree, so ones in stores (and more so, schools) are invariably terrible.
Now, for the topic at hand-
When I was a kid, the two things that would make me gag if I took a bite were sweet potatoes and Brussels sprouts. Lima beans were pretty bad, too. Now, I like lima beans. Sweet taters are still bad, but they won’t make me hurl like they used to. Brussels sprouts are iffy. Sometimes they’re just as horrible as ever, sometimes merely yucky and bitter, and rarely, they approach tasting good.
Cilantro is one horrible thing I never had to endure when I was a child.
Seems the Board is trending towards Celery.