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.