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1.
An absolute requirement when walking around San Francisco.

Opposite of gaydar
Straightdar detects no straightness in the area. User be wary of anus exposure.
by newyorkcitynewyorkstate January 07, 2007
 
2.
the ability to sense if someone is heterosexual.
Bill- "Dude, my straightdar is tingling over that guy you were talking about."

Chris- "Damn it, man. I was definitely going to go hit on his cute ass."
by Ladron June 24, 2010