[lolinder]

As an American who uses it (well, a variant, XD) and knows where I adopted it, I'll hazard a guess: millennial men who were extremely online in the late 2000s and early 2010s, during the Golden Age of phpBB and before the rise of the smartphone and modern social media.

[msephton]

FWIW phpBB was released in year 2000, just to place that on the timeline.