Gov. Chris Christie's 5XL Gym Shorts for Sale

Gov. Chris Christie's autographed workout shorts -- big enough for two, really -- are HUGE ... on eBay.

The seller of the 5XL gym shorts is hawking them as the real deal, straight outta the closet of Jersey's big man. They include a Presidential Physical Fitness Award badge, and Christie's rather ironic signature and note ... "Stay in shape."

Now, Christie's office has yet to confirm the shorts, size 60 waist, are legit and the seller tells TMZ ... she only came into 'em second hand. She says her dad bought 'em for $10 at a garage sale -- where that seller claimed to have won them in a Christie fundraiser raffle.

We did our own comparison of the signatures, and uh ... not exactly a match. At all.

The BIG question, of course ... are they used? The seller makes no promises, but we know this -- ya won't find a single ice cream stain on them.

The Guv's real good with a cone.