LAS VEGAS: One of the oddest moments for Todd Phillips, director of the “Hangover” movies, was meeting a Zach Galifianakis lookalike on the Vegas Strip who refused to have his picture taken if not paid.

Galifianakis' hilarious bearded misfit Alan – who takes center stage in the final installment, out this week – has become a staple image on T shirts and tourist trinkets in Vegas, where the first blockbuster film was set in 2009.

Jobless actors dressed as “Hangover” characters, as well as more traditional movie icons, tout visitors for money to have their pictures taken outside the casinos lining the Nevada gambling capital's world-famous Strip.

“When we were scouting for 'Hangover 3' I saw some guys and I went to take a picture of them. And a Zach character turned around and said 'No free pictures',” recalled director Todd Phillips.

“I said 'I directed the movie, but I don't have my wallet.' But he refused to turn round,” he said.

He was speaking ahead of the May 23 US release of “The Hangover Part 3,”which takes its ill-fated heroes back to the scene of their first mayhem-fueled adventure in Sin City.

The movie, which looks set to be one of the biggest hits of the summer, returns hapless Phil, Stu, Alan and Doug to Las Vegas after they got spectacularly lost in Bangkok in the second installment in 2011

“Bridesmaids” star Melissa McCarthy joins Bradley Cooper (Phil), Ed Helms (Stu) and Justin Bartha (Doug) in a film which starts with Alan's buddies deciding to stage an “intervention” to rescue him from his demons.

Alan initially agrees, but inevitably the plan goes awry, Doug is kidnapped (as in the first two films – “I'm a good Jewish kidnapee,” says Bartha), and the other three have to turn to the crazed Asian Mr. Chow to save the day.

Unlike the previous films the plot does not include a hangover. In those, the story was “reverse engineered” starting with the hapless heroes waking up with the mother of all headaches, and trying to figure out what had happened.

In “The Hangover Part 3” Phillips says he wanted to tie up loose ends from the previous films.

“'Hangover 3' is the ultimate backwards engineering,” said Phillips, explaining how fragments of plot and character which went almost unnoticed are pulled together to “resolve” the hapless friends' story once and for all.

The first two movies broke box office records, and the Oscar-nominated director would love this movie to do the same, even if it doesn't win any awards.

“If you look at the box office … literally a hundred million people have seen (the movies) in theaters alone. That's a pretty cool thing, and I think that ultimately is a more rewarding thing than even an award,” he told AFP.

For the films' stars, the blockbuster success has been spectacularly good news. “Todd has supplied me with the biggest role that any director has ever given me,” said former doctor Ken Jeong, who plays Mr Chow.

Jeong, who again appears full frontal naked in the new movie – which also sees him paragliding over the casinos of Las Vegas and plunging out of the side of a mountain – insists he is shy.

“I'm not an exhibitionist. I'm very shy and very demure about my body, and ashamed about my body. But an actor acts. You've got to make fearless choices to be an actor.” Referring to himself, he added: “I've got nothing to brag about,” and said he cleared the decision to go naked with his wife before agreeing to it with the filmmakers.

He recalled how she teasingly told him: “I guarantee 'Hangover' will be the feel good movie of the summer. I guess every guy will go home feeling good about themselves.”

Galifianakis, whose character finally finds a soulmate in a hilarious scene with the McCarthy, said the Emmy-winning actress's performance is “really nice for the energy of the movie.” The film ends heart-warmingly with the buddies re-united, Alan happy with his new beloved. Well, that's unless you stay past the first few closing credits, when a more typically graphic scene brings down the final curtain.