1 piece of plywood.
mark out a grid of 1 inch squares, leave a 6 inch border around it without squares
Drill pilot holes through the squares so the nails stick straight up when pounded in
Put in spikes, all the same length (buy a 25 pound box at home depot)
Total cost, about $30.
Paint it black.
Spike strips, caltrops = obviously out to damage car.
Bed of nails? "Your honor, if I were intentionally trying to damage a car, I'd use spike strips or caltrops. I had the bed of nails because I found it soothing to lay on it."
THEN, to add insult to injury, take the other guy to small claims court to pay for your bed of nails. (include labor in the cost)
Also, before you paint it black (or green, or whatever matches the ground) lay on it and have someone smash a cinderblock on your chest... get the video and post to ATOT.