Bad blood’s been simmering between “Alias” co-stars Jennifer Garner and Michael Vartan since the sudden end of their sizzling romance in June — which is why Michael EXPLODED when he unexpectedly dropped by the set on a day off and found his private parking space occupied by a car belonging to Jennifer’s new real-life leading man . . . Ben Affleck, the man who’d replaced him in her heart! It was the latest bitter pill Michael’s had to swallow since he and Jennifer — once so hot and heavy they reportedly bought a $1.6 million house together — underwent their unhappy breakup this summer . . . then, in cruel irony, were forced to endure passionate onscreen kissing scenes as the script plunged them into a red-hot affair! So when Michael saw an alien car in his space, he stormed into the production office and bellowed, “WHO the hell is in my parking space?” Angered when told it was Ben’s car, Michael totally freaked when a not-so-swift security guard asked helpfully, “Do you want me to park your car somewhere else?” Eyes blazing, the star ordered: MOVE HIS CAR . . . NOW! Moments later, the security guard rushed outside and parked Ben’s car in another space. Ben then tried to apologize to Jennifer’s ex, explaining he’d been told he wouldn’t be working that day. Michael gave Jen’s Ben an icy stare and snarled, “Don’t ever park in my space again!”