Some of New York’s press corps got a brief break from covering the JFK Jr. story Wednesday night when they attended a sneak preview of Milan designer Gianni Campagna’s soon-to-open boutique above the trendy Cello restaurant. The cocktail event attracted local TV anchors and fashionistas and was followed by a screening of the new “Thomas Crown Affair,” for which Campagna outfitted the star, Pierce Brosnan. Campagna’s sand- and neutral-colored spring and summer 2000 line of handmade neckties (which start at $200) and his handmade suits (starting at $2,000) drew higher praise than the movie.