I am from Costa Rica. As noted above, we have a very conservative culture (prude and full of double standards). Thatīs why I only dared to wear a thong at public places in México (they really donīt mind one bit).
However, I started doing it recently here, because I found out ridiculous to live surrounded by beautiful beaches and not being able to enjoy them as I want.
I did it first at Jacó and more recently in Tamarindo (shown pics). Those two are some of the most crowded, and family oriented. Surprisingly, it was just as if I was wearing dork shorts. I still tried to be at a quiet spot, and as always, taking off the shorts is the hard part, but there was not a single comment, or weird stare during my stay. Everyone was minding their own bussiness and I now have a great time at beaches in Costa Rica.
I had two friends from Mexico that didnīt had such a good experience about thonging here (at Manuel Antonio), so that made me nervous as well, but they are very flamboyant about their thonging, so the did catched a lot of attention.