From my experience as a vegetarian, I found that people took my choice not to eat meat as an attack on their own food choices, so they would get super defensive.
There’s the old joke about how do you someone’s a vegan/vegetarian? Answer: don’t worry, they’ll soon tell you.
This is an issue as some non-meat eaters have a holier than thou attitude about it, and make everything about their choice.
Personally, I never bring it up unless I’m in a food related situation. Having said that, this week I was having lunch with someone I’ve known a while and when they spotted that I asked for veggie options, she made it out like I’d betrayed her for never having mentioned it before, then spent the whole lunch making “jokes” about me being upset at her meat based lunch. I wasn’t upset, but it has shown her in a different light and I don’t think we’ll be meeting up again anytime soon.