I'm not sure how well they'd give people the idea of the full game though. I suppose a better approach might be to take them through a game replay and talk about the strategy and likely communications going on throughout. Even less likely than finding a group of friends willing to sit through a game of Diplomacy would be finding a group willing to sit through a lengthy explanation of the game rather than just jumping in though, so I guess that's likely not such a good suggestion after all.