When I was 20/21 I wore one to the beach all of the time, but I was in much better shape and more physically outgoing then. I wouldn't wear one in public now. Out on my friend's boat or at a private pool party with familiar people... probably.
When I was in my early 20's I had no problem wearing a thong bikini bottom to the beach or water park. Now that I'm older there's not a chance in hell.