1) The sound a thumper makes when it busts off

2) A common adlib used by certain rappers from North Oakland (Lil Rue, HD, etc..)
"Every day it's like I got some new niggas to kill (SMACK SMACK)" - HD on Minister Of Defense / Extortion Muzik 2
by yay area representative March 31, 2011
The more updates name for "sandles" or " flip-flop".
Derrived from the sound the "shoe" makes when hitting your foot.
by Cher-in-Surrey November 2, 2010
Heroin. Most frequently used in the 60s.
When the smack begins to flow, I really don't care anymore...
by Lurhstaap December 29, 2004
To have sex from the back, hit it from behind, doggystyle. Doing this hard and fast so that it makes a smacking noise.
That girls hot, I want to smack that.
by jennw January 13, 2007
usually used while eating some good ass food
by k money bitch June 13, 2017
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!"
by KinnyMcbinspin February 4, 2014