An action akin to the high-five or the handshake. The act of touching fists knukle-to-knuckle in greeting or departure. In 2003 this action was accompanied by the phrase "knuckle-up" but has since just become the motion without the phrase. The first instance of this action and phrase was in Dallas, TX in the mid-90's and has since become a common gesture in most public forms of transit in NYC.
Jimbo-- "Is that some kind of a gang sign?"
Miguel--"Nah, that's a knuckle-up, bro."
A knucklephuck is someone who jacks off with a tightly closed fist. Seemingly stranglingthe penis. It is also slang for guys who think or seem to think with the smaller head.
Will youjust look at those 2 knucklephucks? They don't have a clue as to what they are talking about.