Urban dictionary defines gaydar thus:
The ability/gift of being able to detect homosexuality in other people.
When I was coming out to myself, I would notice gay people in the street or on the train sometimes. I was scared of becoming like them: effeminate, fashionable, and… there was something else. An odd something I couldn’t quite put my finger on that I knew I didn’t want to embody and somehow associated with gayness. I now, however, have a name for it. It is The Wanting Lens. The funny thing is, I assumed that everyone with The Wanting Lens was gay, and did not even consider the multitude of gay men (closeted or otherwise) that passed under the radar completely.