A boy goes to the drug store with his dad and sees the condom display.
Boy:
“Dad, why do they do packs of one condom?”
Dad:
“Those are for the high-schoolers for Friday nights.”
Boy:
“So, why do they make packs of three?”
Dad:
“For the college guys for Friday, Saturday and Sunday nights.”
Boy:
“Then why do they make packs of 12?”
Dad:
“Those are for married couples — you know, January, February, March.”