Mark Cuban Clowned By Mavs Player ... You Dress Like Crap, Bro

Mark Cuban -- swag game weak.

The Dallas Mavericks owner is havin' a tough week -- first, he loses to the Clippers ... and now, one of his own players is blasting his fashion sense.

Chandler Parsons went to Twitter to try and social media shame his boss -- posting a pic of Cuban in a Three Commas t-shirt, a pair of dad jeans and some sneaks ... with the caption, "NBA needs a new dress code for owners."

BTW, we didn't think the shirt was thaaaat bad.