A father and his son go into the grocery store when they happen upon the
condom aisle. The son asks his father why there are so many different
boxes of condoms. The father replies...well, you see that 3 pack?
That's
for when you're in high school. You have 2 for Friday night and 1 for
Saturday night. The son then asks his father, well what's the 6 pack for?

The father replies, well that's for when you're in college. You have 2
for Friday night, 2 for Saturday night, and 2 for Sunday morning. Then
the son asks his father what the 12 pack is for. The father replies,
well
that's for when you're married. You have one for January, one for
February, one for March......