At the convenience store a boy asks his father:

"Dad, what are condoms for?"
"Well son, you use them to practice safe sex."

The boy:
"Oh yeah! I heard of that in school. But why do they come in three packs?"
"The three packs are for highschool boys. One for friday, one for saturday and one for sunday."

The boy:
"What about six packs"
"Those are for college boys. Two for friday, two for saturday and two for sunday."

The boy:
"But what about 12 packs?"
"Those are for married men. One for january, one for february..."