Being civil does not mean watering down. It does involve specifying the actual problem one has rather than use a general insult like "twit". The word "sanctimonious" is not helpful either, if the meaning is that vegetarians/vegans try to impose arbitrary moral standards on others, it is better to say so explicitly, so we know what the actual position is, and can respond to it. (It's been my experience that vegetarians/vegans I read about in the news fit this description, but those I meet in person generally do not, and it is likely a minority of activists get most of the press.)
Being civil should convey more information. It communicates what in particular you don't like rather than general contempt.
I was inclined to agree with pjeby, but JGWeissman's comment changed my mind.
I have noticed that among philosophers, vegetarianism of one form or another is quite common. In fact, I became a vegetarian (technically a pescetarian) myself partly out of respect for an undergraduate philosophy professor. I am interested in finding out if there is a similar disproportion in the Less Wrong community.
I didn't request that this go into Yvain's survey because I want more information than just what animal products you do or don't eat; I'd also like to see nuances of the reasons behind your diet. There are a lot more shades than carnivore/vegetarian/vegan - if you want to be a vegetarian but are allergic to soy and gluten, that's a compelling reason to diversify protein sources, for instance. I'd also like to hear about if you avoid any plant foods (if you think they're farmed in a way that's environmentally destructive or that hurts people or if you have warm fuzzy feelings for plants, maybe). Here are some questions that come to mind: