Meek Mill -- Dares Car Dealer to Sue ... Y'all Still Selling Shaaady Rides!!

Meek Mill kept it so gangsta when a high-end car dealer threatened to sue him for dissing the guy's biz on social media -- he's now been sued .... still, Meek's response to the dealer was hysterical.

As we first told you ... Euro Motor Sport owner Gene Morales got majorly bent when Meek went on Instagram and accused the South Fla. dealer of "selling expensive cars with salvaged titles and lemons." Meek also called him a thief.

Gene sent the rapper a letter demanding he delete the post or else -- but Meek chose to double down. According to legal docs, Meek fired back in an email ... "You guys still selling cars with salvaged titles. Shaaaaaaaaaady."

It's funny, but keeping it THAT 100 got Meek slapped with a defamation lawsuit.

Meek's lawyers must've told him to tone it down, since the IG is now gone. It's unclear when he deleted it, but nonetheless .... the lawsuit has been filed.