If you've never worked in a bureaucracy (and if not, you haven't missed a thing), you won't get this joke. There is a government document (I used to know its Federal document number) which is a blank page. Or rather, a page blank except for the message, THIS PAGE INTENTIONALLY LEFT BLANK.
A lot of government documents are regularly updated, see, with information added and information subtracted. The relevant pages are then sent to everyone who works with those documents. Pages are removed from the documents and other pages added. If the information replacing that on page 9 comes to two pages, the pages are marked 9.1 and 9.2, for example. If the information replacing that on pages 10 and 11 comes to only one page, the new Page 11 is an official blank page. That way, anyone using the document knows that a page hasn't gone missing and there are no relevant regulations being ignore.
Long explanation for a short payoff:
The second page reads THIS PAGE UNINTENTIONALLY LEFT BLANK.
And the third page reads: THIS PAGE DOESN'T GIVE A SHIT.
So that's bureaucrat humor and now you know all you ever need to know about working in a bureaucracy.
Above: For those who came in late, as a way of drawing attention to my newly-published novel, I've been serializing the Image Book I put together as a way of helping me to visualize Faerie and its inhabitants. Having used up three images in one day, I've got something like a dozen left to go.