My gaydar is the smile. It is pretty much always correct. Straight gays don’t smile huge from ear to ear. Just look at post 1, Obama’s smile. NO STRAIGHT MEN SMILE LIKE THAT. There are extra points for receding hairlines as well as some classic mannerisms we all know.
In both my vocation and, especially, my avocation, I am regularly exposed (no double entendre intended!) to homoerotic males, far above the normal representation in society.
Smile: I have been amazed how consistently true this one is. It is indicative when present, but inconclusive when absent.
Clap: Although not as reliable as the smile, I have noted this as well.
Neither of these is absolutely reliable: Stereotypes exist for a reason; they become problematic when they are ruthlessly applied without any external confirmation. I know a few such males who are almost (not quite, but almost) normal in mannerism and behavior.
I have often wondered how much of this is inherent and how much is cultivated.
In my youth, I did not consider myself particularly masculine. I was a shy nerd; I was civilized and unaggressive. However, the longer I live, the more masculine I feel: Our culture is becoming so androgynous, if not effeminate, it sickens me. I find myself longing for a John Wayne to come along and kick America in its collective arse.
(By the bye, I have never smiled like Soetoro the Joker even once in my entire life.)