See that's just stolen, straight up. I've heard at least three comedians make that joke.
(I, of course, am joking about joke theft, but it is a riff on an existing joke)
I got this one a minute ago in response to this post:
> A man walks into a library, and asks the librarian if they have any books on paranoia.
> The librarian leans over and whispers in his ear "They're right behind you"
I thought that was pretty stellar, compared to what you'd get even a year ago.