'Hangover' star Justin Bartha stays in character off the set

"I have a gambling problem, so Vegas is a dangerous place for me," the actor said during a press junket at Caesar's Palace, where the Todd Phillips-directed comedy was filmed. "I'm not a good gambler. I like to think that I'm a good gambler and I'm a card shark and can play poker well, but I end up losing all my money. I lost 50 bucks once. All in one night."

In the film, Bartha plays Doug, a soon-to-be-wed bachelor who takes a road trip to Las Vegas with his best buddies Phil and Stu (Bradley Cooper Zach Galifianakis) for a blowout party they vow they'll never forget. Alas, when they regain consciousness the next morning in a wrecked Caesar's Palace hotel suite, there's a tiger in the bathroom, a baby in the closet, and they can't remember a thing - particularly where they left Doug, who's due to get married in 24 hours.

Since Doug is lost during most of the film, Bartha wasn't needed for a lot of scenes. He spent his surplus of downtime avoiding the casinos and focusing on staying in character.

"Yeah, I don't have much of a life outside of making movies," said Bartha, best-known as the partner to Nicolas Cage's character in the "National Treasure" films. "So I also like to stay in character no matter what. People think I kid, but I'm not. I stayed around and drank a lot, and I stayed by the pool."

No makeup for this method actor. His character was required to look sunburned and dissipated toward the end of the movie, and Bartha went for the real thing.

And he wasn't disappointed that his co-stars had the lion's - or in this case, the tiger's - share of scenes.

"I was excited to watch the scenes, I'll tell you that," Bartha said. "I've seen the movie twice, and I cannot wait to see it again because I miss half the jokes because everyone's laughing so loud in the theater. So I was kind of preparing for my sunburn stuff half the time. So there was a lot of lying by the pool and drinking while the others were working."

When he was working, Bartha said it was a pleasure to improvise with the rest of the cast and director Phillips, who's helmed such hit comedies as "Old School" (2003), "Starsky & Hutch" (2004) and "School for Scoundrels" (2006).

"Basically, the script (by Jon Lucas Scott Moore) as a whole was great, which is probably one of the reasons I think everyone signed up - that and Todd," Bartha said. "Todd always says most of the comedy's in the casting, so you wouldn't cast these guys and not let them improv. So every day you do the script, and it would just naturally evolve into everyone riffing into something else. And then the more crazy it got, Todd is there as the captain of the ship and just specifies all the comedy into a through line throughout the ship."

Working with a tiger was another story.

"The trainers give you this whole hourlong speech about what to do and what not to do when the tiger's around, and never be this close to the tiger, never pet the tiger. And then after the first take, the trainer's, like, over by Craft Services, and the tiger just kind of wanders off."

As for working in Vegas, Bartha can live without it.

"There's Vegas time, you know? ... So when you're shooting this movie for a month and a half, it's pretty much Vegas time - that's a year and a half."

Still, Bartha admits he's been coming to Sin City since he was 8 years old.