[Sheap]

On the subject of diplomacy I present "Sheap's Mini-Rant: Recommendations for Diplomacy":
1) Don't make any agreements prior to the start of the game.
2) Don't bring alliances or enemies from one game into the next.
3) Do remember to draw a clear distinction between your in-game (role playing) persona and your out of game self. This is especially important if you are planning on lying and backstabbing.
4) Don't let in-game conflicts turn into out-of-game conflicts. Don't let out-of-game conflicts turn into in-game conflicts either. Keep the wall between the game and the forums/real world.
5) Don't trade things in one game for things in another game, or use position in one game as leverage to bargain in another one.
6) If you agree to a trade that requires several steps to complete or is otherwise more than simple gems or gold, you are obligated to complete the transaction once it has begun, even if you change your mind later. If something intervenes (a third party invades the province you were supposed to give away, for instance) you must make a good faith effort to come up with a mutually agreeable settlement.

I don't speak with the force of law... but if everyone follows these rules as well as simple etiquette, the likelihood of hard feelings is much reduced.