While I've noticed vegetarians being lumped in with the other two groups, I've not noticed any real (as in socially acceptable and intense) hostility toward them like the others.
I don't know about elsewhere, but I live in the NW U.S. and here it's pretty socially unacceptable to be vegetarian. People give them crap about it at restaurants just based on their order (even if they haven't brought up the fact that they are vegetarian). Shit, it's so socially acceptable to bash vegetarians there's even commercials that do it; usually depicting a man on a date with some psychotic girl that's flipping out b/c he ordered meat and is therefore committing 'murder'. I dated a vegan girl for a little under a year back in college, she definitely got crap for it all the time. Especially when she wouldn't order anything when people invited her out to restaurants that didn't have any vegan options.
I suspect a lot of that is because most vegetarians aren't actively trying to punish other people for eating meat (or at the very least, maybe because those that do are considered animal rights activists instead.)
I don't know man, I've met some crazy over-bearing vegetarians in my time. I've even had some spend an entire meal lecturing me about what i'm eating. But you're probably right about the latter part, most of the vegetarians that do shit like that usually have some higher cause they've devoted their minds and souls to.
I worked with a girl who was a vegetarian, who was very nice...opposite of your description.
Then one day she came back from lunch with this dazed, happy grin....I figgured she done fallen in love or got stoned or something. Everyone noticed it. Asked her what's happened. Her grin gets bigger and in pure happiness she said...