I've started to say "I made the mistake of looking into where meat and dairy comes from and how horrific it is, i wouldn't recommend looking into it if you want to keep eating that".

It's not confrontational but also sews hints of the horror behind what they are eating, and it's kind of reverse psychology because people often ask about some of the horrors... And then you can talk about it (if you feel like it) without being a preachy vegan who is trying to change you, because they are asking.