It is fairly easy to tell at least here in Thailand. If you are into the bars and what is left of the GoGo bars you know Jomtien Complex and Winner GoGo the “boys” for the most part with few exceptions are gay and most likely fem twinks (yuck), now the problem arises if you use the apps as their photo seldom shows their true nature.
"In the land of the blind the one eyed man is king"