This one would be funny if it weren't so dangerous. In some states, teen drivers are not allowed to have more than 1 or 2 passengers in the car. So to get around this rule, they have their friends ride in the trunk. Doing this at 5 mph to sneak into a drive-in movie is one thing, but doing it during normal driving, especially 65 mph on the highway, is very dangerous. But the teens do it because their perception of the risk is lower than the perceived benefit of transporting their friends.
So California passed a law making it illegal for anyone to ride in the trunk of a car. On its surface, it sounds like a funny law. But when you think of why they had to do it (increase the costs of this behavior), it makes perfect sense.