I don't understand why people come up with all these ridiculous "what if" ideas against autonomous cars as if it's anything new.
It's already exceedingly easy to foul up a human driver. Stand next to a freeway and hold up a stop sign. Drop a foam mannequin from a bridge over the road. Paint some bogus lane lines. Shine a laser at their face.
Any of the above will cause accidents with humans, and you'll be arrested and charged with a felony. Deliberate attempts to compromise autonomous car systems carrying humans inside should be treated no differently.