A friend told me this joke as we were finishing dinner last night.
It seems a father was walking through the drug store with his twelve-year old son, and they happend to pass the rack where the condoms were displayed. The boy, who was already curious about the topic of sex, asked what they were for.
The father knew the "facts of life" speech was coming soon, but the middle of the drug store was not the ideal place for it. He decided to keep it simple: "They're for when a man and a woman want to have safe sex."
The boy saw a package of three. "What are these for?"
"Those are for high school students. One for Friday, one for Saturday, and one for Sunday."
Then the boy saw a package of six: "What about these?"
"Those are for college students. Two for Friday, two for Saturday, and two for Sunday."
Finally, the boy saw a package of twelve. "Gosh, dad, what can these be for?"
"Those are for married couples," answered the father, "One for January, one for February....."