Veal. I never buy it, I never order it. I stopped eating veal in my 20’s (I’m 50 now). I heard how the babies are mistreated on many commercial farms and I swore off eating it forever more. I know of two instances that I have eaten veal since I swore it off. One time at a restaurant in VT, it was ground with beef in the meatballs, and I didn’t know until after the fact. I would not have ordered them if I had known. The other time at someone’s house I tasted the osso bucco before I knew what it was, because my husband was raving about it. These events stick with me, because it means so much to me not to break my promise to not eat veal.
I quit caffeine also, but not to the extreme of the veal example, so I don’t know if it counts. I used to drink Coke (it had to be Coke) daily since I was a young child. In my early 30’s I quit. Coke was my main vice, but I also used to enjoy tea now and then both iced and hot. Restaurants never have decaf Coke or iced tea. When they have decaf hot tea it’s almost always some sort of flavor, which is not my cup of tea. I don’t drink caffeine free Coke much anyway, it’s just not the same.
I do cheat sporadically regarding the ban on caffeine, and I still eat chocolate, so it’s not a complete and total renouncement of caffeine, but considering Coca-cola was such a part of my life, it was a drastic change. My husband is still shocked I did it, and that I basically stick to it.
In my 20’s I gave up dairy for about two years. I even ordered pizza with no cheese back then. I had a lactose intolerance at the time. Lactaid pills helped immensely, but for those two years I just gave up the dairy altogether. I think dairy is bad for us anyway, I have been thinking of banning it in my diet again.