Last day of the week before a holiday, where only the truly committed, attractive employees are still in the office. They are rewarded with fun activities and extra casual dress, normally pajamas are acceptable.
Employee: Can't believe we're going to be the only people in the office tomorrow.
Employee 2: Yeah, it would be nice to have the time off, but at least we get a panjama day.
Employee: Oh snap! That's right. Kinect adventures and sweatpants will make for an amazing last day of work before our long weekend.