xkcd.WTF!?

Explanation ➲

In many media, crimes and conspiracy theories are solved on bulletin boards. "Leads" are attached to the board using thumbtacks, and the leads are connected to each other using string (specifically twine is mentioned), in order to sort out connections and possibilities. There are many systems for information mapping that show entities as nodes in a graph, with relationships represented by connections between nodes.

Beret Guy, eccentric as always, manipulates this by making just such a setup solely to determine where to buy the thumbtacks and string for use in it. The joke is that the bulletin board is entirely self-referential -- without a need for thumbtacks and string to hold and connect things on the bulletin board, there would be no need for the bulletin board itself, but because of the bulletin board's string and thumbtacks, Beret Guy needs the items advertised on it. An additional minor joke may be that the Office Depot store map near the bottom of the bulletin board has markers that are often called "digital pushpins".

In media, characters (especially conspiracy theorists) tend to obsess over these boards, overanalyzing or staring at every little detail to try and make sense of them – Beret Guy may be so obsessed with these string boards that he has been driven to obsessing further over the details of making more of these boards.

The title text continues the self-reference theme: The receipt for the tattoo is tattooed to the person who orders the tattoo, which is the receipt for said tattoo of the receipt. This has happened for real in Norway.

The idea of the receipt being the object you buy, has been used in a rug that used to be sold by IKEA.