Shaq ... WE SAW WHAT YOU DID!!!

Charles Barkley was TRYING to do his usual thing of making fun of the larger female population in San Antonio during Thursday's "Inside the NBA" ... but it was Shaq who had the last laugh.

While Barkley was doing his best impression of big people stuffing their faces with churros, O'Neal realized the motion resembled oral sex ... and decided to mess with Chuck.

"Do it slower, Chuck! Do it slower," Shaq said while cracking up!