Tell me what kind of Television you all watch. I would reccomend recording some episodes of the Simpsons, if your son isn't too young for them, and watching them with him and stopping at the jokes to see if he 'gets' them and to explain them if he doesn't.
OMG! Grinity--I was thinking the same thing (Simpsons!) when I was reading the initial post. My kids really think that everything they know is from the Simpsons (after all my agonizing over schools--all I had to do was buy DVD sets). Common sense, jokes, innuendos...even DS6 gets all the jokes, allusions, etc. these days.
