Mark Cuban -- I REJECT Your 'Hoverboard' -- And What's My Player Doing There? (PHOTO)

Mark Cuban isn't messing around ... he's on the warpath against anyone who dares sell a "hoverboard," and it could be one of his basketball players is about to learn a hard lesson on the subject of crossing his boss.

John Soibatian, Prez of IO Hawk, made the offer Saturday, to give Mark one of his very own. The subtext is great ... Mark just partnered with the guy who owns the patent to the device and has said he's planning on suing everyone who markets a knockoff.

Soibatian apparently thought he could win Mark over by posing with JaVale McGee ... who just signed as center for the Dallas Mavericks -- THE TEAM MARK OWNS!

Mark's response makes it clear ... judgment day is coming. And BTW, what's JaVale thinking?