December 31 is the 365th (366th on leap years) and last day of the year in the Gregorian calendar. The next day is the first day of the year in the Gregorian calendar.
- 1999: "SB-129" and "Karate Choppers" premiered.
- 2009: "Banned in Bikini Bottom" and "Stanley S. SquarePants" premiered in Poland.
- December 31 on Wikipedia