Picture found here.
I wonder how you play diplomatic tennis. I imagine the games go like this:
"Oh, that was a great shot! I was just lucky to be in the right place."
I have never been very diplomatic or tactful myself, so I would probably do poorly at the game. This seems fitting as I also do poorly at regular tennis.
I made a similar connection between the wrong words when reading about Moslems being upset with Danish cartoonists. Everytime I read, "...cartoon battle" and the like, I pictured the Peanuts gang fighting Spiderman or something.