After a close-fought game of Carcassone online at BSW with Jeffy and Urs, we contemplated one more. Urs left to make a phone call and suddenly a person named "Wristshot" joined him/herself to our game, and then asked if it was OK. I'm not clear on online chat/game room etiquette but it seemed a bit rude ...
Jeffy and I made a pact on the sidelines that we'd help each other out as best we could (without making it too obvious to Wristy) and it appeared we were going to be in trouble. The interloper managed to garner beneficial tiles at beneficial times, leaving us worried.
One of Wristy's cities was expanding in the north, with no discernible means for either of us to ingratiate ourselves within its bounds. So being a bit miffed to begin with, and with a streak of cutthroat bastardo developed through many games with Jeffy, I did my best to sabotage that city by placing a tile that would make its completion near impossible.
That was my nasty play of the game and my reward was a end-tile cloister that won the game for me. "You know how it is with nuns ..."