For years you've made a name for yourself by pooh-poohing your friends' fears of eating rabbit (aw, not the fluffy bunny!) and by tucking into sweetbreads with gusto (ew, aren't they some kind of gland?). But it's 2005, and those culinary extremes are now so blasé. How do you keep your edge when the rest of the world is catching up to you? Go to Monument Boulevard in Concord. Not only does every meat market sell more organs than you ever knew existed, but taquerias like Chivo's serve them all on tortillas. Buche, pork stomach cooked in lard, is easy to love. Tripa (tripe) poses no problems. A little more challenging are Chivo's tostadas heaped high with chilled cueritos -- pickled pork skin. The translucent strips of fatty skin are tart and just a little chewy. Not bad with a little salsa verde, actually. Impress your friends and bring some home for them to try.