John Cena Fires Back In $500k Supercar War with Ford

John Cena is giving Ford a little attitude adjustment of his own -- telling the car company to take their lawsuit over his old $500,000 supercar and shove it.

We broke the story ... Ford claims it sold Cena a super rare "limited edition" Ford GT supercar -- 647 horsepower, 3.5L EcoBoost V6 engine with an MSRP of $450,000.

Ford claims they only selected a few people for the privilege of buying the car -- and Cena was one of the lucky ones (Justin Verlander and Joey Logano also own the whip).

The caveat, according to Ford, owners CANNOT resell the car during the initial 24 months of ownership. Ford claims Cena broke the rules and flipped his ride for a profit. They're suing Cena for every penny he got from the sale.

But in new court docs filed in district court in Michigan, John says he did nothing wrong -- because the final contract he signed said nothing about a 24-month no-resale clause.

Cena says Ford screwed up by not putting the sale restriction in the final binding contract -- and he shouldn't be punished because they suck at paperwork.

Now, he's asking the judge to throw out the case against him.