I remember once in Public Press game where I began the game allied (I was Germany) to England and Italy.
It was a crazy game on many levels, and I do believe that I fought everyone at some point, but they thing that really annoyed me was this.
England went CD inexplicable part way through. He was being doubleteamed by France and Russia so I tell the new guy that we'd make natural allies. And of course the bugger doesn't respond beyond a "look, I'm screwed", rushes into the low countries, and promptly is killed while I have a two year setback.
Fastforward a while. The only powers left are myself, Italy, Russia, and Turkey. Italy (the most powerful) and I are contemplating attakcing the others when suddenly he gets banned for multiaccounting (in another game). Quickly, a new Italy joins. I suggest some moves. What does he say? Nothing, he just inexplicably goes on an all-out offensive against me. Gah!!
Despite these annoyances though, I was later vindicated.