Blue Tooth Finger
The blue tooth finger is the obnoxious finger raised by an individual engaged in a phone conversation on their blue tooth headset.  It generally occurs when an innocent bystander happens upon the blue tooth talker but cannot see the blue tooth device.  The bystander unwittingly responds to the phone talker who then raises the blue tooth finger indicating that they are on the phone and not speaking to innocent bystander.  The bystander thereafter feels a strange combination of embarrassment and anger.    
Tom: I thought some guy at the grocery store today was talking to me.  I responded to something he said, but then realized he was on the phone when he gave me the blue tooth finger. 

Ed: That’s embarrassing.  Were other people around?

Tom: Yeah.  Plus, he gave me a dirty look like I should have known he had that stupid thing in his ear.  