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.