The true night before Christmas. It is spent getting so intoxicated you feel like shit on Christmas day. The origin is believed to date back to the Victorian era when adults would give their excitable kids some alchohol to make them sleep easier, however, they soon came to realise they were missing out big time and made it an adult tradition instead.
"What did you get for Christmas?" - Dave
"I don't know. I had a rough Christmas heave and didn't open my shit yet" - John