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As a sometime vegetarian, it is probably helpful to ease social occasions with meat-eaters by bringing your own plate of "meat substitute" and letting them know that you'll only be having the vegies. I know many vegetarians/vegans who are a bit arrogant and so probably would help for them to reassure meat=eaters they are not being holier-than-thou.
Well, I suppose I'm biased about this, being a vegetarian, but I think I've met more arrogant meat-eaters than vegetarians. After 15 years of being asked why I don't eat meat, I don't care to discuss it in a social setting, but when it comes up in conversation people often want to heatedly defend their own choices to me, with no prodding (believe me!) on my part. Although I have strong feelings about it - factory farming is pretty gruesome, not to mention its impact on climate change - I'm not out to "convert" anyone, unless they genuinely want guidance on how to eat a healthy veg diet.
That said, I'm always happy to discuss it if the question is presented in non-judgemental way, and I'm a HUGE cheerleader for people who are reducing, but not eliminating, animal products. It doesn't have to be all-or-nothing to be worthwhile. So I guess my point is, regardless of your thoughts on vegetarians, it's good to approach the topic respectfully. it sounds like most of the people responding here do, but I've encountered plenty of people who don't.