Before the Shitty Add-On standard, there were several independent conference badges with their own hats and add-ons. The 2016 Queercon badge came with hats, powered by two small expansion ports on the top of this cuttlefish badge. The expansion ports provided power, ground, and an I2C bus on a 1x4 connector, giving these cuttlebadges unicorn horns, an emo haircut, or a top hat studded with LEDs.
In 2017, there was an obvious need for a standard for badge-addons, with even more standards created. Luke Jenkins published the MiniBadge standard for SaintCon, an impressive standard that implemented 5V, 3V3, I2C and SPI in less than a square inch. The results were impressive, with more than a dozen minibadges being built for the main SaintCon badge.
Finally, we come to the 2017 / DefCon 25 AND!XOR badge which featured Hunter S. Rodriguez and a Futurama Brain Slug.The schematic for this Brain Slug is very simple, just an ATtiny85 microcontroller and a handful of WS2812b LEDs. It's blinky, it's bling, and since every board house can do green solder mask, you can make a Brain Slug PCB pretty easily. Only about ten or so of these Brain Slugs were ever made (although the Gerbers are right here so knock yourself out), but it was a precedent for add-on bling.
DefCon 25 came and went, and a few lucky people walked away with Brain Slugs. Some time around February, 2018 -- the time of Chinese New Year, because that's obviously the best time to start any sort of electronic project -- a few members of the Badgelife collective started asking a few questions. The previous two years of badgemaking showed everyone add-on badges were a thing. The future would have minibadges, or other weird PCBs hanging off the big badges. What if there were a standard for Badgelife add-ons? What if these pieces of indie electronic art could host Brain Slug-like add-ons from multiple creators? The AND!XOR badge really only supplied power to the Brain Slug, but adding holes for pin headers on a badge is effectively free. The only thing you need for this is for the entire group to come to an agreement on a standard pin out.
After literal minutes of discussion, we had a standard. it was decided that the Shitty Add-On pinout should include 3.3V, Ground, and an I2C bus on four headers arranged on a 0.1" grid. The badges would have female sockets (or just through-holes), while the add-ons would have male pins. This is the first, and only, official documentation of the electrical and mechanical specifications of the Shitty Add-On standard. No one followed the standard, but everything worked out in the end.
Why do I say no one followed the standard? Because I'm an idiot. After using Microsoft Paint for three minutes, I whipped up a quick board that would supply power to four Shitty Add-Ons. It's the Shitty Add-On Totem, available on OSHPark. This board is as simple as it gets, with two AA battery holders and four 2x2 headers. The design is pretty clever; two of the headers are rotated 45° clockwise, the other two headers are rotated 45° counterclockwise. This means more add-ons will fit on your totem.
Because the first publication of the Shitty Add-On standard was.... lacking... I whipped up a quick improvement. The headers (now self-documenting on the PCB with the addition of a silkscreen circle) were copy and pasted from the OSHPark render of the Totem. This, unfortunately, is the documentation everyone used. No, the headers were never meant to be rotated forty five degrees, I was just lazy and didn't rotate what I copied and pasted from the OSHPark render. But even if the mechanical properties of the Shitty Add-On header were incorrect, at least everyone got VCC, GND, SDA, and SCL in the right place.
The foundation was set for inter-operations between badges and add-ons. The standard was finalized in February, with Def Con a mere six months away. Dozens of PCB artisans would create their own Shitty Add-Ons. The Official Def Con 26 badge supported the Shitty Add-On standard. The best estimates of the production of badges per Def Con attendees say this: At Def Con 26, there were approximately 25,000 attendees. There were approximately 50,000 badges and add-ons that supported the Shitty Add-On standard. By any measure, Shitty Add-Ons are a successful standard. Hundreds of different Shitty Add-Ons were created. Most of them had LEDs. One was a game of people eating Tide Pods on the Blockchain.