No experience nor thoughts have been given to the subject by me on the question or situation posited by OP prior to reading this thread but as I went through the comments it seems key that the law assumes everyone's intentions are puritan with respect to a person flying a drone in airspace wherever it flies. I would think the same puritan intention would be assigned to someone that flies another object at the same time...meaning the person whose privacy is being invaded. Some ideas...
Instead of using another drone at $300 minimum to take out the snooping drone, would an RF controlled helicopters be able to reach the same height as a drone? If so, why not "accidentally" bump into his drone's propeller blades? Or similarly, why not go out and fly a kite and accidentally get tangled up with the drone if the wind cooperates?