An intuitive sense that enables someone to identify whether another person is gay.
I think my Gaydar is broken.
If you are someone other than a straight female living in Sydney, you may require a translation. Gaydar: the technical term used to describe the way in which heterosexual women discern whether a man is homosexual. Also known by its more colloquial name: Queen Meter.
Mia Freedman, "Sydney unzipped," Sun Herald (Sydney), August 18, 2002
The pick-up area is confined to the west part of the heath, a clearly defined dell cut off from the rest by a main road. Within it, formal, if perfunctory, courtship rituals were being performed among the bare trees. Men meandered with studied slowness along the paths, waiting for eye contact from passers-by. When their ''gaydar'' told them that an assignation was on, they went up short, well-trodden tracks, strewn with foil condom wrappers, which led straight into the undergrowth.
Nick Cohen, "Out in the undergrowth," The Independent (London), March 15, 1992
She's gay? Bi? How come my gaydar hadn't picked up on it? Maybe the flashing of her breasts in my face had been deliberate.
—Margaret Cruikshank, The Lesbian Path, Double Axe Books, January 1, 1981