From a general perspective, you can't control other people. You can't control what they're going to say. To be at the mercy of another person's words to be able to completely bring you down or send you into a fury, you're really just exposing how vulnerable and sensitive you are. Offense is taken, not given. You can be impermeable to those words if you really want to.

While you can't control others or what they do, you do have full control over yourself and how you respond to others. You live in a world and culture dominated by an ideology that isn't inline with your own. I would recommend working on your coping skills so you aren't angry and clenching your fist when someone asks you if you enjoyed something before you were vegan or mentions eating meat in front of you. Not only will it be good for your mental and physical health, but it will also help give vegans a better name if you're welcoming and friendly to general discussion, instead of being triggered by the mere mention of something you used to do or mention of something that goes against your current beliefs.

If it really bothers you that they ask you about eating meat, or mention that they're going to eat meat, I guess say something to them asking them to stop or whatever. But I think it would be a lot better and more productive if you could get over your aversion to discussing it. It sounds like you have a perspective that could contribute to a meaningful conversation about it.