... It's your birthday.

This rule is an oldie but goodie. Everyone knows that calories don't count on your birthday, but they might not know the science behind the rule. It's pretty simple- aging is a highly calorie-intensive process. It takes thousands and thousands of calories to turn a year older because of all the changes associated with growing up. The culmination of a year long aging process occurs on your birthday, and uses up more calories that anyone could physically consume in a day. Because of this, the anniversary of your birth is scientifically predetermined to be a negative calorie day, no matter how much you eat. Therefore, to safely avoid passing out, you must eat a much as you can. If you don't eat all of the cake, candy, burgers, pizza, and other goodies offered to you in celebration, your next birthday could be your last.

 My mom's calorie-free day! She turned 35! ;)

 One more thing- a lesser known, but related calorie rule is as follows: on your birthday, the calories consumed by your friends and family only half-count. Meaning of the 2,000 calories worth of birthday cake they consume at your party, only 1,000 calories count! This is because your loved ones burn a lot of calories throwing you a party, buying you gifts, and generally attending to your every need. It's a safe bet that at least half of their calories are used up throughout the day. So let them know that in addition to wishing you a Happy Birthday, they should be saying 'Thank You!"