Forget the old line about comedy not getting any respect.

Director Todd Phillips single-handedly demolished that perception with his raunchy 2009 blockbuster "The Hangover," which grossed a staggering $468 million worldwide, making it the most successful R-rated comedy of all time.

Now Phillips is back with "The Hangover Part II", which opens in U.S. theaters and much of Europe on Thursday.

Once again, the movie stars Bradley Cooper, Ed Helms and Zach Galifianikis (and a scene-stealing, drug-dealing monkey). But this time it's dentist Stu (Helms) who is getting married, in Bangkok. Predictably, more mayhem and bad behavior ensues.

Successful comedy sequels are notoriously tricky to pull off. So how did Phillips approach the project?

"I know expectations are high, but liked the idea of the challenge," Phillips said. "I knew I'd have this great cast again who're willing to try anything I come up with, so why not give it a shot?"

Commercial hopes are also hefty. Despite mixed early reviews, some industry projections see the Warner Bros. movie bringing in more than $100 million at the North American box office alone on its opening weekend.

The formula remains much the same -- after another blackout and some appalling revelations (including a severed finger, a shaved head and hermaphrodite hookers) the guys try to figure out exactly what happened the night before.

But the location has changed from Las Vegas to the appropriately hot and steamy back alleys of downtown Bangkok.

"Vegas was the perfect setting for the first one, and almost like another character," said Phillips. "When you say 'Vegas,' it sounds like trouble to most people. And if you say 'New York,' it sounds like a lot of different things to different people. But 'Bangkok' to me means, there's going to be a lot of bad decisions made. So it felt like natural progression -- or digression."

Early reviews say the sequel is almost an exact copy of the original. Variety said the new movie was "little more than a faded copy of its predecessor" but the Hollywood Reporter said that "what happens in Bangkok isn't as much fun as when it happened in Vegas, but it's still worth the trip."

MONKEY BUSINESS

So were the cast nervous about returning to the scene of the crime?

"There's pressure. You can't escape that thought because it occurs to everyone, including us. There's some apprehension but then, once you're in the trenches, making the damn thing, all you're trying to do is make the best movie possible," said Helms.

Much of the plot revolves around a chain-smoking capuchin monkey, played by movie veteran Crystal, whose impressive credits include "Indiana Jones and the Kingdom of the Crystal Skull" and the "Night at the Museum" franchise.

She stole the show.

"I would say don't ever work with kids or animals except for Crystal because she's a serious pro. Hits her marks, knows her lines," Helms said.

Her only problem? "She's got a smoking habit which we hope she kicks but, it's cool," Cooper joked.

But Crystal's on-screen chain-smoking was no joke to animal rights campaign group PETA, which slammed Phillips after he stated that "the hardest part of making the movie was teaching Crystal to smoke."

"I was just joking but they freaked out," said Phillips. "The truth is, the cigarettes are fake and all the smoke is digital."

The comedy also attracted controversy when Mel Gibson was forced to withdraw from a cameo role because of bad publicity and Hollywood reaction over his widely publicized telephone rantings last year to his ex-girlfriend.

"It was a horrible thing to have gone through just because Mel is such a gentleman and Mel is actually a friend of mine," said Phillips.

Rumors that former U.S. President Bill Clinton was also set to appear in a surprise cameo, were just rumors.

"He happened to be in Thailand when we were shooting, and I did angle him for (a cameo) and he's like 'Absolutely not.' That was not going to happen, but him and his secret service guys stopped by the set one of the days," said Cooper.