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 04, 2014