Squishing your bare ass cheeks against a window (preferably an eating establishment with seating right at the window) and shitting. While shitting, you ensure the proper smearing technique is used to create a pastel effect on the window.
When I was 8, my Dad and I went to get a poutine and chili dog. On the way home he introduced me to the art of the squished hamburger on the window at Mel's Diner. I plan on passing this gift for generations to come.