Well the term would properly and fully be “Gay Detection and Ranging” which sounds like something Fred Phelps and a stereotypical depraved homosexual of lore would both try and patent, but what do you dopers think it is.
I mean gay people don’t have a stamp on their forehead which declares them to be so. I ask this because apparently it is something I lack or so I was told today.
It is the ability to discern whether a given person is more hetero- or homosexually inclined. The word is especially used in a situation where you’re looking for a hook-up. For instance, gay men who have properly adjusted gaydar don’t waste their time (or, God forbid, get beaten up) by chatting up heterosexual men.
There’s a belief (and this is among gay folk, not something the religious righties came up with) that it’s possible for someone with “good gaydar” to be able to tell when someone else is gay. And it IS possible, but not because of some kind of echolocation via three-snaps-around-the-world or whatever. It’s just recognizing certain signals that are unconsciously sent by the person…a man’s eyes lingering over another man longer than a straight man’s would, subtle flirting, etc. I can’t even enumerate the actual things that are picked up on with gaydar because so many of them aren’t even being recognized on an individual level…it’s more of a gestalt of all these things mixing together.
It’s obviously not some telepathic or mystical thing, and it’s obviously not 100% correct at all times (or, for some people, at all…I’ve always tended to get a lot of false “wishful thinking” results…), but it exists.
If they did, you wouldn’t need “gaydar” to detect the closeted ones.
It’s like any form of humans being able to see beyond the surface of another person. Sometimes it’s easy to tell when someone is lying or when someone is hiding something. We do this subconsciously, and when we do it with gay people, then “gaydar” is a perfectly cromulent word to use (even if I hate the word "cromulent).
Not a bad idea, though. How about a stamp that is invisible to the naked eye, but can be detected through the use of a special polarized lens? We could call the glasses Gay-Bans.
A gaydar-equipped person may not even know how they do it.
In situations where you have clear feedback on whether your guesses are correct, but little clear data to reason from, you can develop unconscious pattern-matching.
ETA: I’m not saying gaydar is “real” per se, but some people are clearly better at guessing than others, and probably most people would do better than random chance.
Go to your room!
Right now!
FWIW, I can’t think of a use of this term meant in any serious sense. It seems to have two ironic/humorous uses:
One is where someone perceives “gays” all around them from clues so tiny only they can see them, usually ridiculous or imaginary ones. “His gaydar’s turned up a little high.”
The other is where someone is completely oblivous to an evidently gay person who’s perhaps flirting with them - “His gaydar needs a little work.”
But never, “Wow, Bob, *great *gaydar… I never would have figured that waiter was gay.”
As a gay man, I don’t think too much of the term gaydar. As you pointed out, it’s a very stupid portmanteau. I don’t use the term myself.
That being said, it’s fairly easy to tell if a guy is gay or not if you’re trying to figure it out surreptitiously. Not all gays are super obvious, but unless a gay guy is doing everything in his power to fool you, he’ll give it away eventually.
As another poster already mentioned, it’s mostly in the eyes/smile. You can honestly just tell by the way a guy is looking at you while you’re talking to him, or by catching him looking at someone in a way that you recognize, if he’s interested sexually. Just like how you could tell if a guy was really digging a woman he was talking to, you can tell if a guy is really digging talking to another guy.
In that sense, the guys who are able to tell other guys’ sexuality from subtle cues tend to be pretty attractive themselves. It’s easier to tell someone’s sexuality if you yourself are attractive because people treat attractive people differently.
Of course you can also go by the way a guy talks, moves his hands when he talks, emotes, dresses, etc, which can all be helpful in figuring it out. But mostly in the eyes and the smile and the way he talks and interacts with other (usually attractive) guys.
Edit: Now if someone was actually pointing out to you that you have bad gaydar, you probably missed someone who was obviously gay… like “flaming” if you care to use the term.
Gaydar is indeed real and it’s not entirely due to mannerisms. “Gayface” has been scientifically proven:
http://www.nytimes.com/2012/06/03/opinion/sunday/the-science-of-gaydar.html?_r=0
Do I have to explain everything!
portmanteau - I had to look that one up. You learn something everyday.
IIRC someone a few years ago came out with a device called Gaydar. Some sort of wrist electronic device that would tell you if another person was wearing one and their direction and proximity. Someone should make a phone app.
Capt
After a quick search there is a phone app
They have that. It’s called Grindr.
I prefer scruff.
Well, I was going for “generic gay hookup app” rather than “gay bear hookup app”. But yeah, Scruff or Growlr for me, although Scruff annoys me, mostly because of “Johnny Scruff”, who seems to think he invented bears (and defined them as mostly hairy twinks).
I think you can buy them at the Sharper Image.
I still think my “Gay-Bans” idea from post #5 has merit. 
gay people don’t have a stamp on their forehead but they should have a hanky in their pocket.
Yeah, I’ve seen the hanky chart. I took a checkered paper napkin from an Italian restaurant one time to blow my nose, wadded it up and shoved it into a back pocket, and the next thing I know a Brazilian albino dwarf was asking me if I wanted to play “horse”.