I hated asparagus when I was a kid, because all I’d ever had was frozen asparagus (which has a weird texture and an off-taste) or disgusting mushy canned asparagus. When I finally tried fresh asparagus as an adult, I found I actually liked it, though only if it’s good asparagus in season (I still won’t touch that frozen or canned crap).
Artichokes don’t travel well, and are another vegetable that shouldn’t be eaten out of season. If Happy Wanderer’s friend grew up somewhere far away from California (where almost all artichokes sold in the US are grown), it’s not too surprising that he never had one, or if he had had one, it might not have been very good- artichokes can be bitter, and bitter artichokes are nasty.
Brussels sprouts are another vegetable that I hated as a kid, but like now. But only fresh brussels sprouts (none of that abomination that is frozen brussels sprouts) in season, and not overcooked like most people tend to do them. They don’t have that strong sulfurous taste or icky mushy texture if you don’t overcook them, and without those, they can be good.
It’s hard to find good avocados in some parts of the country, too- my mom (in western Maryland) has a terrible time finding decent ones. I don’t even know if the markets near her carry pre-made guacamole. Maybe that’s why those kids had never had them?
Maybe some people who are dealing with picky eaters should try getting fresh, in-season vegetables instead of frozen or canned, and try cooking them in different ways, to see if the picky eater will like them better another way? The quality of vegetables can make a huge difference for a picky eater.
Or try frozen vegetables instead of canned, or vice versa- I like frozen peas (especially with pearl onions or, even better, caramelized onions- mmmm…), but hate canned peas (because of the weird taste and disgusting mushy texture of canned peas). And there are picky eaters who like cooked vegetables, but not raw ones (I’m one of those- the only raw vegetables I like are avocados, mushrooms, and non-iceberg lettuces), even though the reverse seems to be more common.
And to picky eaters out there- it might not actually be some food that you dislike, but the way you’ve had it prepared.