A father and a son happen on the condom aisle at the grocery store.
The son asks his father why there are so many different boxes of condoms.
Well," the dad replies, "you see that three-pack? That's for when you're in high school. You have two for Friday night and one for Saturday night."
"What's the six-pack for then?" asks the youth.
"Well," the father answers, "that's for when you're in college. You have two for Friday night, two for Saturday night and two for Sunday morning."
"What's the twelve-pack for then?"
"That's for when you're married," says dad. "You have one for January, one for February, one for March..."