A person who doesn't play by the social rules in a online game. Originated in the Sandbox mod of Battlefield 2, to describe "retarded" players who "smacked" people with props and did generally douchebaggy things. Akin to the Mingebag of Gmod.
Smacktard - "Lol I pwned your ramp with my Stunting DPV"
*Smacktard places explosive barrel at the bottom of a large ramp that you spent 5 min. building*
*Smacktard loads a huge dildo, crashes the server*