((Work in Progress, help appreciated))
Origin
On July 3, 2012, tumblr user cardiganponi made a post titled “IMPORTANT MESSAGE ABOUT BRONYCON ORGY” [1]. The message in question was to warn other bronies about the possibility that crabs was contracted by several members of the orgy.
Spread
Rumors and speculation about whether or not the orgy actually happened spread quickly, along with several posts confirming that it did in fact happen.
External Links
[1] Tumblr – "cardiganponi – IMPORTANT MESSAGE ABOUT BRONYCON ORGY
[] Tumblr – tagged – Bronycon Orgy