It's like that with some of my friends. I NEVER bring these things up in conversation, but they'll ALWAYS offer the argument, then get pissed off at my retort. I don't mind being asked questions or anything (except really stupid shit like, "Would you kiss a girl if she ate meat?". I don't care what I have to do, as long as I get to put it in before I drink myself into a fucking stupor!), but it usually begins with them waving a piece of meat in my face and going, "Mmm... steak..", like I'm going to snatch it off their fork and revert. What the fuck?
I don't even bother mentioning it at all during conversation with strangers. It's completely self-defeating, and every other vegetarian I know does the same.
I'm not out to change the world, as I had enough difficulty in changing myself.