By DCist contributor Celeste Dawn Mitchell Two thousand of the khaki crowd’s finest came out to party Thursday at Friends of the National Zoo’s Young Professionals’ (or FONZ YP’s, if you will) sold-out Brew at the Zoo. Proceeds went toward its Asian elephant conservation project. Just in case patrons forgot they were partying for a cause, four-ounce fill-lines on souvenir mugs intimated that this was a classy tasting affair, not a frat kegger. Though…