Most people I know don't discover I'm veggie till they offer me a bite of something. I'm not stuck up about it, nor do I advertise it.
This is not to say that I don't think there are sound ethical, economic, health and ecological justifications for my dietary choice, and I'm happy do discuss them if someone shows an interest.
I also believe that Toyota makes better quality products than General Motors, but, again, I don't push this opinion on people.
I suspect meat-eaters, when confronted with vegetarians, sometimes feel a bit guilty and seek to justify their choices. Denigrating those whose opinions, habits or culture discomfit you is a tried and true ego defense mechanism.