This question is prompted by a paragraph in Randall Munroe's what if? post the other day entitled "What if New Horizons hit my car?" (in turn based on a question by Robin Sheat). The answer to that question was, "it would be pretty bad for both vehicles," although as is so often the case it's not so much the answer but the explanation.
But as long as we're talking about the answer, it would in fact be pretty bad. The New Horizons spacecraft weighs over 1,000 pounds (478 kg), and is about the size and weight of a concert grand piano. And while it would be bad if a grand piano hit your car, it'd be worse if the grand piano were traveling at over 30,000 miles per hour. (That's almost 50,000 kilometers per hour, but somehow kph is still less impressive.) Moving at more than eight miles (or 14 km) every second, New Horizons is one of the fastest objects the species has ever created.
And you parked right in front of it. Nice job, genius.
Oh, also, it's powered by a nuclear generator, so the tiny pieces of your car that are now on their way to the Kuiper Belt are also radioactive.
Randall included a couple of legal points in his analysis, concluding that—and this is the good news—(1) NASA would have to pay for your car and (2) because you wouldn't be at fault, in most states your insurer would be legally prohibited from raising your premiums. I think those answers are both right if we assume, as he does, that your car was parked at home and New Horizons was rather dramatically off course. I want to assume, though, that your car was orbiting Pluto.