I can almost always spot the gay man (men) in the room. Maybe it's due to all the experience, having grown up in a family that owned a florist for many years - almost everyone who worked there was gay.

I don't know how I know, and I have tried to analyse it. I think that in general the brain recognises patterns that it is not even aware it is recognising. So when you have enough patterns (as gay people do, and as perhaps as some people who spend a lot of time with gay people do), you can mostly identify, even if you are not sure how you do it.