The word “flexitarian,” meaning someone who mostly eats vegetarian with the occasional cheesesteak thrown in, has been around for a while. But only recently have former vegetarians been so smug about their forays to the dark side. “There is something almost primal about it,” writes lapsed vegetarian Tara Austen Weaver, describing her first meat-buying expedition in “The Butcher and the Vegetarian.” “I haven’t actually hunted dinner myself, but I set my sights and claimed the prize I sought.” The “primalness” of the meat-eating (or meat-purchasing) experience comes up a lot in these conversion narratives, which inevitably take place at a quaint, family-run butcher shop.