These are things you can do on a long road trip if you get bored. Also a great short story by Orson Scott Card. I don't endorse actually playing any of these games however. Read the story to find out why.

-Blue Angels: This works best on two lane freeways. Come up next to a car in the other lane doing about the speed limit and match their speed. The cars behind you can't pass, and hilarity ensues.

-Follow: Pick a car and follow it. No matter what they do stay on their tail. This is a great way to fuck with random people, although I guess it could be considered a little mean. I do this whenever someone passes me on the freeway, since I'm usually doing 80 anyway, I take it as a challenge. Especially if they pass me on the right, I hate that.

- Chicken: If you and a friend are taking separate cars somewhere you can play this. Basically whoever dares go the fastest wins. This is a major display of balls if the area happens to be full of highway patrol.

Those are the only ones I could think of for now. Add your own if you have any.