What do four of our greatest actors do when they have down time between meaty roles? They get together for an inconsequential comedy about four old friends who travel to Las Vegas for a senior citizen version of “The Hangover.” The plot: Billy (Michael Douglas, 69), Paddy (Robert De Niro, 70), Archie (Morgan Freeman, 76) and Sam (Kevin Kline, 66) have been best friends since childhood. So when Billy, the group’s sworn bachelor, proposes to his thirtysomething girlfriend, the four head to Vegas with a plan to stop acting their age and relive their glory days. There are a few predictable laughs as each man brings to Vegas — and overcomes — his respective emotional baggage concerning love, sex, loyalty and freedom, but for the most part this comedy just coasts along from one mediocre set piece to another. Extras: Commentary with director Jon Turteltaub and writer Dan Fogelman; three featurettes: “It’s Going to Be Legendary” behind-the-scenes look at the production of the film with commentary from the main cast, “Four Legends” look at the ensemble main cast and their insights on working with one another, “The Flatbush Four” glimpse at the character arcs of the four main characters. Blu-ray adds three more featurettes: “Shooting in Sin City,” “The Redfoo Party” and “Supporting Ensemble.” Vitals: Director: Jon Turteltaub. Stars: Michael Douglas, Robert De Niro, Morgan Freeman, Kevin Kline, Mary Steenburgen, Romany Malco, Jerry Ferrara. 2013, CC, MPAA rating: PG-13, 105 min., Comedy, Box office gross: $60.586 million, Sony.