losing with class
For agencies, losing a client sucks, especially when it's a cool client with lots of money. But unfortunately it happens, and when it does you can either go all Don Draper on 'em with a crafty public letter or you can end the relationship with class.
Taxi in Toronto chose the latter when they recently lost the Mini account by auctioning off their boardroom Mini on eBay with all money going to support a local homeless shelter. They even accompanied the auction with a well-written, kind note about the time they spent working on Mini.