ROCKY start for Sly Stallone after he arrived in Italy to film “Avenging Angelo” — then roared off in a stranger’s car in a scene right out of “Driven”! The star exited a trattoria after a business lunch, spotted his leased car as a valet drove it up, hopped in — and BOOGIED!! Problem? The car, although identical, WASN’T HIS! The valet ran screaming after Sly, but he didn’t hear — and moments later, the REAL owners were screaming at the valet! Meanwhile, after driving a few blocks, Stallone said to himself, “YO! This car ain’t MINE!” He floored it back to the eatery and confronted an enraged Italian couple — whose mouths dropped open when they recognized the superstar car thief. They calmed quickly when Sly apologized — AND signed autographs!