Smack On means to propose a fight with someone. Generally in a joking manner but can definitely can be used very effectively in a real situation. Smack On is closely associated with the term "punch on".
Joking:
Luke: "You suck apples"
Brad: "Smack on cunt"
Serious:
Josh: "I fucked your ex on a trampoline!"
Ryan: "Smack on cunt!"
Luke: "You suck apples"
Brad: "Smack on cunt"
Serious:
Josh: "I fucked your ex on a trampoline!"
Ryan: "Smack on cunt!"
by KinnyMcbinspin February 4, 2014
 Get the Smack Onmug.
Get the Smack Onmug. by liv May 13, 2005
 Get the smackmug.
Get the smackmug. by Bigg Phill January 30, 2010
 Get the smacks ofmug.
Get the smacks ofmug. by Sickyle January 28, 2003
 Get the smackedmug.
Get the smackedmug. by Smackedboi October 27, 2009
 Get the Smackedmug.
Get the Smackedmug. First invented (allegedly) by Dan Mace. Means let's get things done. A whole episode of 368 by Casey Neistat is titled after this phrase "SMACK IT."
by Amycrackpot May 28, 2018
 Get the SMACK itmug.
Get the SMACK itmug. 