class birthday – n. the theory in which your group or class has a particular day that is a “birthday” of the group. It was discovered in davepoobond’s 7th Grade Math Book. It’s really fucking stupid, and has no relevance to anything.
The following is the quote from the 7th Grade Math Book:
“What is the ‘birthday’ of your class? To find out, find the number of days each student has been alive. Then average the number of days you have each lived. With this average, work backward to find the average date of birth for your class. Plan a celebration for the ‘class-birthday.'”