Similar to gaydar, this is the sixth sense many men possess which helps them to determine exactly how crazioactive a woman is.
Two guys at a bar:
Guy One: Ok dude, let's see what we've got going on tonight
Guy Two: Alright man, let me turn on the Guyger Counter
Guy One: What about the redhead?
Guy Two: No-go, still broken up over her last boyfriend
Guy One: The blonde?
Guy Two: Severely insecure because she's been a bridesmaid in 6 weddings, is nearing 30, and hasn't been in a steady relationship since she was 19
Guy One: Short skirt?
Guy Two: Jealousy issues.
Guy One: Ok, what about Glasses over there.
Guy Two: Hmm...I don't know. I'm getting a low reading, possibly within safe parameters. She's probably not too crazioactive. I say go for it.