movie daydream
Whenever im on a long trip in a car... or just generally bored. I tend to pick up on some word or idea off a billboard or some sign and almost instantly form an entire plotline to a bad B movie in my head, along with who i would get to play for each part.
Personally, I like picking three random people sitting near each other on the subway and writing a script with them as the main characters-- as if the subway is the first scene.