Diplomacy. It's interesting that the movement (and support) mechanics are easy, it's the social aspects that are hard.
The fun thing is part way through the game you can suddenly find that you are a cylon and have to switch sides.
The D6 generation is a good podcast that covers a lot of games both board and minatures
I wouldn't quite call it "the game that ruins friendships", but since it places a lot of emphasis on the social aspects of the game, rather than the strategic, it involves lots of lying and backstabbing, which can (understandably) strain relationships between the players.
And in my experience, good Diplomacy players do very little lying or backstabbing. The compulsive liar types can't get the strong alliances that lead to traction. A two or three way alliance that culminates in a later betrayal are the way to win.