A 12 year old boy was in a store with his dad.  When they passed the stand with condoms the boy asked his dad what they were.

The dad said, "Those are condoms, you use them when you want to have safe sex."

The boy asked, "Why are there only three in that pack?"

Dad said, "Because they are for high-school boys.  One for Friday, one for Saturday, and one for Sunday."

The boy pointed at another package, "Why are there six in that package, then?"

The dad said, "They are for college boys.  Two for Friday, two for Saturday, and two for Sunday."

Finally they boy asked, "And the twelve pack?"

The dad gets a bit tearyeyed.  "Yes my son, those are for married men.  One for january, one for february, one for mars..."