Seems like there should be an x-ray or some test-

Zubin Jelveh at Portfolio is onto some striking new research:

How long does it take to decide if a man is gay?

It turns out that people make their decisions within 50 milliseconds of seeing someone, and that first instinct is accurate the majority of the time, according to research by Nick Rule and Nalini Ambady of Tufts University who have a study in an upcoming issue of the Journal of Experimental Social Psychology.

Via BPS Research Digest (emphasis mine):

Twenty-two male and sixty-eight female undergrads were presented with photos of 90 men's faces (half were homosexual) for either 33ms, 50ms, 6500ms or 10,000ms. The anonymous photos were taken from an internet dating site where posters stated their sexual orientation. Any photos featuring facial hair, glasses or jewelery were not used.

At 33ms, the presentation was too quick for the students to consciously 'see' the faces and, perhaps unsurprisingly, their ability to determine the men's sexuality was no better than if they were simply guessing. However, at 50ms - just long enough for the faces to be consciously seen - the students' accuracy grew to 57 per cent, which is significantly better than chance performance. Accuracy didn't increase with the longer exposure times, suggesting that all the relevant information for making the judgment had already been extracted by 50ms.

In a second study, the researchers guarded against the possibility that the men in the dating photographs had deliberately accentuated their sexuality. This time photos were taken from the social website Facebook, where they had been posted by people other than the subjects of the photos (so deliberate accentuation of sexuality was less likely). Again, from just a 50ms exposure to men's faces, the 15 undergraduate participants were able to recognise the men's sexual orientation with an accuracy better than chance.

But that 57 percent success rate means that almost half of the guys initially perceived to be gay aren't. But I'm sure none of you fine readers has ever been guilty of that. I know I haven't...

What's needed is a followup study to explain why Republicans and evangelicals have such poor gaydar: