I'm not sure where this started, but I know it started way before I married DH. My MIL and her sister are hilarious together. I think one time when they were at a family gathering they started singing and used their zippers as the "music". So, now every time they are together we request a performance. A couple of years ago we all made them these shirts so they would have a costume. They just have a zipper sewn to the front and some rainbow ric rac around the collar. They wear big huge sunglasses, and then they added the lovely hair ensemble. The song they sang was "When the Saints Come Marching In." The kids were all cracking up and had a great time watching their grandmas be silly together.