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1.
The art of completely raping the enemy team with vehicles in games such as Halo and Unreal Tournament 2004. Often linked with roadkill.

Also an announcement in UT2004, which is played if you squash an enemy in the Manta. This is where the phrase originated from.
t3h_sniper: "headshot j00 fag!"
Xan: "Die, bitch!" *squashes t3h_sniper*
Announcer: "VEHICULAR MANSLAUGHTER!"
by Kouen June 11, 2006