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1.
A spurious ping on the gaydar. Those utterly heterosexual folks who consistently (and generally unknowingly) trip queer folks into thinking they are also gay or lesbian.

Although not in any way limited to this list, heterosexual men who are

1) faintly swishy in behaviour or
2) well-groomed and attired or
3) remarkably toned and muscular or
4) wearing a luxurious mustache along with a military fade haircut
may all end up as false positives.

Although not in any way limited to this list, heterosexual women who are

1) faintly masculine in behaviour or haircut
2) prone to sensible shoes or flat-heeled boots
3) often in charge
4) not drowned in cosmetics
5) softball players
may all end up as false positives.

The term carries no pejorative weight. Gaydar is a finely-calibrated instrument, can be easily thrown off, and no blame is assigned either to the hapless straight or to the wondering queer when a false positive is discovered.

(slang term, queer subculture, noun)
"Look, Martha, I know Betty's a hot softball coach, but she's married and monogamous and straight. Give it up. She's just a false positive."
by Miselaineous October 19, 2009