So, XKCD is not actually all that funny in itself. Trying to "find a joke connecting panels together" is the wrong way to digest XKCD. The joke in this case is

So, XKCD is not actually all that funny in itself. Trying to "find a joke connecting panels together" is the wrong way to digest XKCD. The joke in this case is the same as most of the Beret Guy jokes: He has some sort of alien view of the world which has mired him in a 9-year-old's mentality, so that when we see him appear we are seeing an overly literal concept of what the adult world is about. The humor is not "ha-ha" funny so much as a mind-state of vague bemusement. This may be the reason XKCD has been so successful. By offering a comedic "buildup" which is insufficient to generate a "release" of hysterical laughter and all of the neurotransmittery goodness that comes with that, you are left trawling the archives for more and more humor.