“When did casual sex become a crime?” asks Matthew McConaughey in this lively romantic comedy. A photographer infamous for his womanizing, he gets an unexpected answer to his question when the ghost of a playboy uncle (Michael Douglas, enjoying himself) visits on the eve of a family wedding and advises him to mend his callous ways. Writers Jon Lucas and Scott Moore steal from the best, gleefully cribbing from A Christmas Carol to fashion a screenplay with heart and sharp one-liners. Jennifer Garner is sweet and radiant as McConaughey’s childhood friend and former lover; Lacey Chabert steals scenes as the woman marrying McConaughey’s brother; and Robert Forster and Anne Archer are good as her parents. Mark Waters (The Spiderwick Chronicles, Mean Girls) directed. PG-13, 115 min.