Here's how the transformation happened.
First, I laid it out on my cutting board, and drew a straight line, just above the bottom pockets, with a piece of chalk.
Once I got that cut off, I cut off the sleeves, leaving about a half to a fourth of an inch there on the vest, which will soon be frayed to get that shabby look. Then, I cut off the buttons and the button holes up to the collar. It took me a while to decide if I wanted the collar or if I should chop that off too.
Lastly, to perfect the magic shabby look, I threw it in the washer, then in the dryer. I had to clean out the lint tray a few times. Small sacrifice for the outcome, I say.