Ask the Big Kahuna "Answering the most common visitor questions"

Response:

Aloha DJR -

According to the State of Hawaii, nudity is illegal at all state beaches. But if you ask a local, you will find out that there are quite a few beaches that are well-known for being "clothing-optional" or "nude." Due to a case in 2000, there is still some debate as to whether it is really illegal to sunbathe and swim nude. Before you head out to the beach, make sure that it is a well established "clothing optional" beach, because the police don't hesitate to enforce the no-nudity rule.

Since nudity at the beach is illegal, we cannot endorse it. However, beaches that have been known to be "clothing optional" include these:
Big Island: Honokohau Harbor Beach, Kehena Beach (Dolphin Beach), Steam Vents.
Kauai: Donkey Beach, Secret Beach.
Oahu: none.
Maui: Little Beach at Makena (Pu'u Ola'i Beach), Red Sand Beach in Hana (Kaihalulu Beach).

When in in doubt, Big Kahuna says: Keep your shorts on.

Mahalo for your question,