December 1: Eat A Red Apple Day

December 2: National Skip School Day

December 3: National Green Bean Casserole Day

December 4: National Cookie Day

December 5: Bathtub Party Day

December 6: World Trick Shot Day

December 7: National Illinois Day

December 8: National Brownie Day 

December 9: National Llama Day 

December 10: Festival For The Souls Of Dead Whales

December 11: Worldwide Candle Lighting Day

December 12: National Ding-A-Ling Day 

December 13: National Cream Cheese Frosting Day 

December 14: More Good Today Day

December 15: National Cat Herders Day

December 16: National Chocolate Covered Anything Day

December 17: Canadian Maple Syrup Day

December 18: Answer The Phone Like Buddy The Elf Day

December 19: National Emo Day

December 20: National Steven Day

December 21: National Short Girl Appreciation Day

December 22: National Cookie Exchange Day 

December 23: National Laura Day 

December 24: Last-Minute Shoppers day  

December 25: National Pumpkin Pie Day

December 26: National Thank You Note Day

December 27: Make Cut-Out Snowflakes Day 

December 28: National Call A Friend day  

December 29: Still Need To Do Day

December 30: National Bacon Day 

December 31: Make Up Your Mind Day

Cites: 

http://nationaltoday.com

http://www.jazzhostels.com