You learn how to do Vehicle Attacks a few missions into the start of the game.
I believe we already met the conditions for this challenge so no one should feel the need to grind this.
Over a hundred people have earned the "Full Throttle" achievement since the start time (Oct. 12th) which is for getting VA's. That achievement is also for getting Dino Attacks and I'm not sure if those count but I'm gonna assume people probably do way more VA's than that one achievement requires and if you look at the leaderboards for the game page some people have pulled off thousands of VA's by them self.
So to make sure you get credit for this challenge simply kill a single enemy with a Vehicle Attack and check to see you got some percentage in the "Full Throttle" achievement either on the Achievement app on the console or the games page here on TA.
The challenge should unlock for everyone a couple days or so after the challenge time expires.
Update: Five days later it unlocked for future reference and what will likely happen with all other community challenges for this specific game.