It didn't originate in online gaming as has been suggested, and has actually been around since the mid 1990's.
Smacktard defines a drug dealer selling drugs or, as some forms are known, smack, that also happens to be a retard.
It has recently been embraced by the world of podcasting after being introduced to 'Punky Radio by Kaje.
You are a smacktard.
You are all smacktards.
Sam is a smacktard.