Gordon Ramsay says the only thing that's full of s*** is the TikToker who started the social media smear campaign against his restaurant.

We caught up with the celebrity chef in New York City on Tuesday ... and he's calling BS on the viral video.

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ICYMI, a customer complained that a dog took a dump on a pee pad inside the London location of his Street Pizza restaurant. But an eyewitness said the same as the chef ... the pup didn't actually go to the bathroom at all.

Gordon tells us they've reviewed the CCTV footage and "under no circumstances" did the dog drop a deuce ... over even pee, for that matter.

Gordon's chalking the whole thing up to overexaggerated clickbait -- and said dogs are still welcome at his pizza spot ... just so long as you keep 'em outside on the terrace.