There's nothing more satisfying than...Destroying someone who does all the following during the game:

1) Allies with someone early on, only to break his alliance and destroy him when he starts losing to finish at a higher place.
2)This person, weak with 4-5 territories but not totally helpless, then allies with the strongest person on the board and cowers in a corner.
3) The tides start to turn and myself and my ally start gaining a little ground on the strongest person on the board.
4) After it is clear that either me or my ally will win, the person pleads with the both of us not to kill him.

People like that piss me off. Of course, he was dealt a decisive blow and he ended up in fourth place, losing points.