Although I've always wanted this particular superhuman power, I've never been very good at detecting other men's sexual orientation. Findings from a recent study published in the Journal of Experimental Social Psychology, however, suggest I may be underestimating my gaydar abilities.
The January 2008 study investigated people's ability to identify homosexual men from pictures of their faces alone. In an initial experiment, researchers Nicholas Rule and Nalini Ambady from Tufts University perused online dating sites and carefully selected 45 straight male faces and 45 gay male faces. All of these photos were matched for orientation (only faces shown looking forward were used) and facial alterations (none of the images contained jewelry, glasses or facial hair). To control for context, the faces were also cut and pasted onto a white background for the study. These 90 faces were then shown to 90 participants in random order, who were asked simply to judge the target's "probable sexual orientation" (gay or straight) by pressing a button. Surprisingly, all participants (both men and women) scored above chance on this gaydar task, correctly identifying the gay faces. Even more surprisingly, accuracy rate was just as good when the images were exposed at a rapid rate of only 50 milliseconds, which offered participants no opportunity to consciously process the photo. (read Scientific American article)
Reasons to want to know if someone is gay: if they want to openly flirt with the person (probably number one), how openly they may talk about taboo subjects, approaching personal space, might want to introduce them to a friend ... and very superficial reasons like telling jokes or not, asking their opinion about their shoes, inviting a person to a Eurovision party (look it up if you don't know what it is). Or...a girl is hoping to make a gay male friend who they can be close with without things getting sticky or complicated. And of course...natural curiosity.
Yes...many people can tell if someone else is gay...even if they do their best to hide it. Yes...there are some gay people who think their gaydar is 100% right...sometimes they just wish a guy was gay...sometimes they think a well dressed Italian must be gay (they would be more wrong than right). Some people don't even recognize a gay guy who is screaming to the world wrapped in an atomic rainbow. Some gay people obsess over this and it's probably not healthy. Some straight people obsess over it (probably equally not socially healthy). Some people obsess over how people put people in slots and generalize too much.
I don't think it's inherently bad to be curious about it. I do think it's unhealthy if it becomes an obsession or if the reaction would be an emotionally charged one if they don't like the answer or if someone is hyper generalizing people of a sexual orientation. It's a totally appropriate topic of conversation in an open forum such as this.