The act of putting your right hand palm up, flicking the middle finger back and forward whilst saying "BONG!" to vulgarly arouse a young girl or boy.
Can also used to intimidate a friend or PE teacher by "bong fingering" their rectum or testicles.
Gaz : "How can I arouse the potential Ryan?"
Ryan : "Use the Bong Finger!"
Gaz : "BONG BONG BONG"
Potential : Oooooohhhhhh.... *orgasms*