the reason you would short the car battery is because you're trying to pass too powerful of a current through too weak of a wire.
also, it would be dangerous to try, you could possibly hurt the person terribly and as they said earlier, practical jokes are meant to be . . . anything but mean. if the victim isn't laughing after the prank, it wasn't a good idea . . .
just use a smaller battery, that would be easier to conceal.