I spent the day at Starbucks with my laptop. At the end of the day, after I felt like I did something pretty productive, I headed out to my car thinking to myself, "Good job, let's go home and make some original music."
I essentially had the 3 chord progression and beat already arranged in my head before I even got to my car and almost everything else you hear in this track before I got home (and I live one block away from Starbucks). The bridge took a day or two to sleep on. A VERY rare "instant arrangement" indeed!
Image source: http://www.flickr.com/photos/crypteria/43986807/