I think the best way is to get them to play a few games and incorporate game theory into movies/tv shows they already know. Here are a few ideas:
1. Dollar auction game
A dollar is auctioned off to the class. The winner gets the dollar, but the hitch is the second highest bid has to pay but gets nothing. This game demonstrates the ideas of best response and irrational escalation. It hints at why political campaigns and lawsuits (both all-pay auctions) get overly expensive. Article on http://mindyourdecisions.com/blog/2008/09/09/business-drinking-and-the-dollar-auction-game/" from my blog.
2. Game theory in the Dark Knight
There were a lot of game theory concepts in this Batman movie. I wrote about http://mindyourdecisions.com/blog/2008/08/19/game-theory-in-the-dark-knight-a-critical-review-of-the-opening-scene-spoilers/" .
3. The Ultimatum game
There is a pie of size 1. One person offers a split and the other can agree to it or not. If agreed the split goes through. Otherwise they both get nothing. The game theory solution is that the proposer can take most of the pie. In practice this is not possible because people get offended by low offers. There's a cute video of http://mindyourdecisions.com/blog/2009/11/03/the-ultimatum-game-played-by-children/"
4. http://mindyourdecisions.com/blog/2010/03/09/how-las-vegas-casinos-use-the-prisoners-dilemma-to-make-money/"
This is a real-life example of a situation resembling the Prisoner's dilemma. My friend was playing a poker tournament. A $65 buy-in gave 2,500 chips, but for $5 more you can get 3,000 chips. What do you do? Obviously you buy more chips at a lower cost. The hitch is that this extra $5 does not contribute to the pool of winnings--it goes directly to the house. Everyone would be better off by not buy extra and dilute the chips, but no one can enforce this so everyone buys in extra and everyone is worse off.
Hope these examples help!