HPMORverse is actually a simulation being run at some higher level of reality

The funny part is, we know this to be literally true. The less-funny part is that it is incredibly difficult for an author to write himself into his own story as a character without coming off incredibly hokey. Heinlein mentioned himself in passing a couple of times and it wasn't any worse than any other in-joke, but I know of no better examples than that.

Edit: I have, of course, forgotten Godel, Escher, Bach. Not sure how. That's a bit of a special case, though.