Although I have ocassionally preferred not to explain inside jokes, I think I will go the other route by explaing the joke, not really giving any explanation at all and making fun of myself for doing that.
So the joke was: when I became a grown-up with an office of my very own, I planned to have a picture of the Rey-Osterrieth complex figure hung up and framed on the wall with the rest of my art. If anyone asked me about it, I'd "Go ahead and draw it, then I'll tell you where the tumor is" but then the TV show "House" came made being Mr. "Hi! I'm a person who can rudely deduce that you are going to die based on seemingly unconnected symptoms that are actually connected after all" seem a whole lot less funny.