As above, Little Beach on Maui is very fun and I've found thongers there each time visiting >> South of Wailea, in Makena State Beach, there is a nude beach that is popular with gay locals and tourists called Little Beach. Out Traveler has called it one of the top 5 nude beaches in the country
On Oahu, Diamond Head Lighthouse Beach
https://hawaii.gaycities.com/beaches/50005-diamond-head-lighthouse-beach. Closer adjacent to Waikiki is Sans Souci Beach also called Kaimana Beach
The Royal Hawaiian Hotel beach area right on Waikiki is thong friendly with a more toned and tanned crowd
I usually stay at the Halekulani Hotel on business trips and have thonged at the pool. But I'm not so shy about it.