Originated on tumblr around the same time commenting "ZOMG I CANNOT B R E A T H E!!!!!!!!!! XDDD" was an acceptable response to anything even mildly or vaguely funny. I think the v a p o u r w a v e / aesthetic meme normalized it and then it found it's way to the regular internet-goer
I don't have an issue with it and i use it myself on platforms where there are no italics/bold options, in situations where all caps isn't necessary but you still need to emphasize some level of emotion on a word.