To be honest, alcohol. I didn't "get" drinking until basically once I graduated college. I drank, sure, and I threw up a couple of times, but my problem was essentially that I didn't know my limits or how to moderate my drinking, and as a small person my max capacity is usually about - oh, six drinks. So if I drank in college I was pretty guaranteed to have a bad time, or not drink enough (like, have a beer) in order to hit that sweet spot of "I'm drunk and I'm having a great time." It was either "I'm mildly buzzed and can't tell" or "God I'm miserable and I've been pouring poison into my body and WHAT ARE YOU DOING WITH YOUR LIFE _refugee_???"

Coffee I've grown into but don't love, still. Like kb, tomatoes - I love my tomatoes now but used to be completely uninterested.

There are some tastes I identify as "adult tastes" that I think some people grow into as their palates mature and evolve - dark chocolate, for instance, and coffee is another one.

Can we do "things you used to love but now hate"? That one's easier. :)