The first one that comes to mind is sushi. My mom has always loved it, but it made me gag until I was about 20. A boyfriend at the time convinced me to go to a local sushi restaurant and I went begrudgingly and got the beef teriyaki, but after a few visits, he managed to get me to try a piece of his sushi...I was hooked.
And it's weird, because he was the last person you'd ever expect to like sushi. He was a big, burly, truck-driving country boy that had grown up in a really rural part of GA. Yet, the man loved sushi. He and I long ago broke up, but I still go to that same sushi restaurant at least once a week, haha.
I also did the reverse for cucumbers - I loved them when I was a kid, and now I can't stand them. They taste like soap to me. No idea what happened.