Expanding on the Baron's advice about aiming at the man rather than the machine, what about aiming at those devices which either assist or replace the man?
Whether grav, ducted fans, or other agency, "flying" cars are going to have some sort of "fly-by-wire" component in their operation. A flight computer and/or avionics suite of sorts is going to really control the vehicle, translating input from the "operator" in a way that ensures the vehicle isn't placed outside of it's flight envelope. Add in the various hi-tech, hi-pop, and/or hi-law "traffic control" measures already raised and there will be more ways for this "fly-by-wire" system to further constrain or even prevent operation of the vehicle.
Such systems are going to require sensor inputs for various things like air speed, altitude, pitch, yaw, roll, inertial location, and so forth. A GPS-style system could provide most if not all of those inputs but there would most likely also be systems onboard the vehicle as back-ups if nothing else.
Even relatively "primitive" flying vehicles have onboard sensors. There's a pitot tube mounted on every Cessna, for example, which provides the pilot with their air speed indications. The tube is small enough to be easily damaged with a pistol butt or other object. While some pilots might still take off without the pitot tube working, those pilots who want to live to fly another day generally think twice.
I'm wondering if tampering with the onboard sensors linked to the flight computer/avionics suite might be the same as shooting out all four tires, smashing a distributor cap, cutting a serpentine belt, or any of the other classic ways of disabling a car. Look at the "breathlyzer" interlocks placed on the steering wheels of habitual drunk drivers. They need to blow into the device before the car will start and, if the device isn't working or has been tampered with in anyway, the car won't start at all.
Using the pitot tube analogy, I wonder if damage to a discrete sensor bundle or bundles might stop a "flying car" from taking off altogether? The pilot powers up the vehicle, the avionics systems first boots then queries it's flight sensors, determines those sensors aren't working, and shuts the vehicle down.