http://reddit.com/u/1R0NYMAN came up with what he thought was a genius strategy to get free money via options trading in this thread.
The autists of r/wallstreetbets were mixed. Some of them thought it was genius, others, however, actually understood what they were talking about and strongly advised against this strategy.
Less than a week later, this thread pops up from http://reddit.comu/1R0NYMAN with the results mentioned in my title. Almost a 2000% loss.
It doesn't stop there, though. Around the same time, Robinhood (the app used to make these trades) sent an email notification out to users that the trading strategy used by http://reddit.com/u/1R0NYMAN was no longer being supported by the app, with a strong possibility of his loss being the direct cause.
But it gets more interesting. As http://reddit.com/u/WOW_SUCH_KARMA points out here, Robinhood may be legally liable for the losses due to some of their actions / lack of actions.
Now, the entire subreddit is exploding with memes and quality shitposts about the entire situation, and the latest news is that http://reddit.com/u/1R0NYMAN has been contacted by MarketWatch, a stock market news site that may want to run a story about it all.
Who knows where it'll go from here.
EDIT: Because people keep asking, it's hard to get a firm understanding of what exactly happened without at least some knowledge of how options work, but this is a good place to start for an ELI5.