National Ugly Christmas Sweater Day began in 2011, though people have been having fun with this for a lot long.
“In 2014, they partnered with Save the Children in their ‘Make the World Better with a Sweater’ campaign.”
https://nationaldaycalendar.com/national-ugly-christmas-sweater-day-third-friday-in-december
My oldest daughter’s family LOVES to wear ugly sweaters during the holiday season. Honestly, it has become one of my favorite traditions, especially since they have encouraged my youngest daughter’s family to join them. It just adds a new level of cheer to the spirit of the holidays for me.