In my last game I got so annoyed by the apostolic palace always taking resolution to end the wars I started that I built boats and a stack, navigated all around the continent, and then DoW the guy that had built it. Smart enough, I razed his city, effectively preventing the AP to ever stop my war again.
Next thing I know, the following turn someone else built the UN... Fortunately it was on the same continent, sameside just a little north, so I put my stack back in my boats, moved it north, DoW this other civ, and razed their capital aswell, effectively removing the UN from the game. Then I proceeded to kill everyone for the next few hundred years with a big grin on my face. It was a pretty satisfying feeling.