Pajama day

A day, usually on a weekend or during a day off, when you have nothing to do and sit around lazily in your pajamas, not leaving the house. Often involves eating cereal for every meal and excessive television/video games.

Speaker 1: "Hey, want to go see a movie?"
Speaker 2: "No way man, I'm having a pajama day. Let's just sit around and watch Seinfeld reruns."