Slut-ometer

The innate sense that most males are born with that tells them who is a slut, who isn't, and how much of a slut that person is. Often expressed with beeping noises.

Dude 1: Look at that chick wearing the tube-top!
Dude 2: Slut-ometer is on!
Dude 3: beep-beep-beep...
(girl gets closer)
Dude 3: BEEPBEEPBEEP