Actually, I'm pretty sure it has roots in the YABDL crowd over on Fetlife. I've been active for a while, but I've lurked for longer and IIRC, it was a direct response to the utterly atrocious spelling/grammar that used to infect message boards and such (I know that hasn't completely vanished, but it used to be much, much worse).
Similar targets of scorn were missives like the, "RU Poppy" or "wet/messy dippers" messages some of our finest minds would incessantly throw at people from their basement dwellings. Over time it became slang, then people figured it was as good a substitute as any to discuss in public. Hence it took on a life of its own.