There are pockets of nude use around the island of Oahu, but they're very small and you have to know when to go. The most reliable de facto C/O beach is just north of the old polo field in Mokuleia near Haleiwa on the "North Shore". You can see the hulk of an old airplane in the middle of that field in Google maps' Satellite View: In maps.google.com, search on "Hawaii Polo Oceanfront Trail Rides, Oahu, Hawaii" and then switch to Satellite View. "Polo Beach" is just east of that as the shoreline curves back out to sea. There is a trail to the beach from Farrington Highway that passes through the least developed land that you see along the shoreline. "Polo Beach" is where the pine trees are the thickest.

~Reggie~