Folks on social media are trolling the actor for his appearance in a recent advertisement for Crypto.com ... the mean Tweets are flying Thursday, as the crypto market loses a whopping $200 BILLION.

Matt's catching heat for his infamous "Fortune Favors the Brave" commercial for the blockchain-centered technology ... which started airing back in October, when the crypto market was humming along.

But, with the market crashing, people are piling on Matt ... with many pointing out anyone who bought crypto due to Matt's ad is now taking a bath.

Here's what some of Matt's haters are saying ... "Matt Damon was in Oceans 11, 12, 13. You crypto guys just fell victim to his latest heist." Others are wondering who will play Matt in a movie about the Bitcoin collapse.

Matt's commercial was for a website where folks could buy different kinds of crypto, including Bitcoin and Ethereum, both of which are crashing.

Larry David and other celebs have been pushing crypto in recent ads ... but it seems Matt is the easy target.

In the last 5 days, the largest cryptocurrency -- Bitcoin -- has lost more than 17% of its value. And, it gets worse ... over the last 6 months, Bitcoin has lost more than 50% of its value. Less known coins are getting annihilated ... some losing more than 90% of their value.