I don't understand those novelty plastic scrotums that people attach under the back of their cars. What are you trying to say with that? Do you want me to imagine your car having sex? Because now that's all I'm thinking about. More importantly, if we get into an accident because I rear-end you, would it be considered rape?
People with those car balls are probably people who loved the Pixar film Cars. I'm pretty sure in the world of that movie, cars procreate like humans. It's the only explanation. There aren't any people around to build the cars, because everybody is a car in that movie. There are little bugs shaped like cars, there are cars watching other cars race each other, etc. It makes no sense.
Toy Story works so well because it's somewhat based in reality, the concept being: "when you leave the room, your toys come alive and have crazy adventures!" Cars has nothing like that. But they could fix that simply by adding one last shot at the end: we see the cars drive into the sunset past a half-buried Statue of Liberty, their balls flapping in the wind. It was earth all along!