Dwayne Johnson is a man of his word, and so is one of his biggest fans ... 'cause after a chance meeting at a store, the guy got the WWE Superstar's autograph tattooed on him -- and now he's getting a free ride to WrestleMania!
Johnson was shopping at Target last week when he ran into Ruben Rodriguez, a lifelong fan, and his young daughter.
Rodriguez told Johnson that if he signed his arm, he would make it permanent .