The act of slamming the back of your partners head like a gameshow button while recieving oral. The reaction to performing the whammy button is usually a buzzing sound, much like you were actually on a gameshow answering questions. The other most probable reactions are either a slap to the face, or your partners dinner on your balls.
"Hope you don't mind if i hit the whammy button sweetheart". "Okay, no whammy, no whammy, no whammy, no whamm- STOP!"