a greeting given to a male adversary consisting of grabbing him by the balls and squeezing as hard as possible until he doubles over in pain, then headbutting him in the bridge of the nose.
"If you think he's too big to take down otherwise, give him the old Irish Handshake, he'll be on the ground bleeding before he knows what hit him."
Guy 1:"dude how drunk were you last night?"
Guy 2:"Drunk enough to get a Irish Handshake"
Guy 1:"Sick!! From who?"
Guy 2:"I was so drunk I don't remember her name"