What happens in Vegas stays in Vegas. But the crazy antics in "The Hangover" could turn Bradley Cooper and co-star Zack Galifianakis into the toasts of Hollywood.

There's the buzz that lingers after a wild night on the town. Then there's "The Hangover." Todd Phillips' new comedy hasn't even hit theatres yet. But its early buzz could prove just as lasting and a lot more pleasant.

"We got very lucky in this movie and it's all because of having Todd at the helm. I think this is his best film yet," co-star Bradley Cooper told CTV.ca.

Rolling into theatres on June 5, this rollercoaster ride stars Cooper, Ed Helms, Justin Bartha and Zach Galifianakis as best buddies headed to Vegas for a bachelor party.

So what you say? Been there. Done that.

Ah, not like this you haven't.

The madness that ensues on this bachelor blowout would make a drunk's wildest holiday look tame by comparison, and much easier to explain to a fuming bride.

• CTV.ca Trailers: The Hangover

Remembering nothing of their first night on the town, these boys awake to find their $4,000-a-night luxury suite at Caesar's Palace trashed and filled with meandering chickens.

There's a screaming infant abandoned in the closet. After a few more blinks of their bloodshot eyes they see an enormous pet tiger belonging to boxer Mike Tyson.

Worse still the groom (Bartha) is missing. Groomsman Stu (Helms) discovers that someone has absconded with his gleaming front tooth. There's also a hospital bracelet wrapped around the wrist of good-hearted groomsman Phil (Cooper).

When the hungover travellers try retracing their steps, their valet ticket produces a Vegas police car instead of their own wheels.

Stu's quickie wedding to a pole dancer (Heather Graham) is soon unearthed. Mike Tyson plays air drums singing Phil Collins' "In the Air Tonight. Nuts, right?

What really happened nobody knows, not until the final credits roll. But their search for answers sends Cooper and crew on a blisteringly funny mystery hunt that would make Jack Black pale.

Add to that the surefire breakout performance of 39-year-old Zach Galifianakis, who plays the bride's gonzo brother, and this "stays-in-Vegas" caper will surely boot past those city's limits in quick time.

Think of what Judd Apatow's "The 40 Year Old Virgin" did for Seth Rogen. That's what this sleeper hit will do for comedian Galifianakis.

If "The Hangover" is a box-office winner, as so many critics are predicting, it could also signal Cooper's leap from character actor to full-fledged movie star.

"This movie is completely hilarious. But it's really a detective story," says Cooper, 35. "Every scene that's there is essential for this mystery to work. The chapel scene, the emergency room scene, the 'Rain Man' sequence...You couldn't take that stuff out and have this movie work."

Of course, matrimonial mayhem is nothing new to the 34-year-old American actor.

Cooper gave a fine turn as Rachel McAdams' sociopathic boyfriend in "Wedding Crashers" (2005). He also held is own opposite Jim Carrey in the 2008 comedy, "Yes Man."

Earlier this year Cooper starred as Jennifer Connelly's philandering husband in "He's Just Not That Into You."

Playing the funnyman, however, is not what Cooper calls his forte.

"I'm not even funny at all. That's what's so ironic," the striking star told Details magazine in its June/July issue.

With two more features expected later this year -- Sandra Bullock's comedy "All About Steve" and the long-delayed Renee Zellweger thriller, "Case 39" -- rumours are swirling that Cooper will play Hal Jordan in the upcoming adventure flick, "The Green Lantern."

"I know nothing about that," smiles Cooper, who will likely appear in the sequel to "The Hangover."

"I don't know if they have officially announced 'Hangover 2.' I know Warner Bros. loves the idea. We'll see," says Cooper.

Adding to his growing fame is recent press surrounding his rumoured relationship with "Friends" star Jennifer Aniston.

"I have met her three times in my life...My mom loves it, but unfortunately it's not true," Cooper told People Magazine in May.

Cooper married actress Jennifer Esposito in December of 2006. The couple divorced in 2007 after four months of marriage.

"I don't know what lies ahead," says Cooper. "Some people say the guys I play are jerks. Like Phil, for example. You think he's a jerk because he takes money from rich kids in the movie to get to Vegas. But he's not. His buddies are everything to him."

With so much emphasis on bromance flicks these days, Cooper says what men can bring to comedies leaves far more room for play.

"The male struggle with his sensitivity and relationships is investigated in a lot of comedies up until this point. I don't think 'Hangover' fits into that entirely. It's an aftereffect of the movie," says Cooper.

"You go along on the ride. You learn about the guys. You see they're not so bad at all."