Story of one I went on once:
Celebrating his upcoming marriage to Tracy Garner (Sasha Barrese), Doug Billings (Justin Bartha) travels with his best friends Phil Wenneck (Bradley Cooper), Stu Price (Ed Helms), and Tracy's brother and Doug's future brother-in-law Alan (Zach Galifianakis) to Las Vegas in Alan's father's Mercedes-Benz for a bachelor party, staying at Caesars Palace, where they relax in the room and go to a casino and celebrate with few drinks on the hotel rooftop. The next morning, Phil, Stu and Alan awaken to find they have no memory of the previous night, and Doug is nowhere to be found. Stu is missing a tooth, their hotel suite is in disarray, a tiger is in their bathroom, a chicken in their living room, and a baby is in the closet, whom they name "Carlos". They find Doug's mattress impaled on a statue outside of their hotel and when they ask for their Mercedes, the valet delivers an LVPD police cruiser.
Following clues to their steps, the trio travel to a hospital where they discover they were drugged with rohypnol ("roofies"), causing their memory loss, and that they came to the hospital from a chapel. At the chapel, they learn that Stu married a stripper, Jade (Heather Graham), despite having a long-term relationship with his mean-spirited girlfriend, Melissa (Rachael Harris). Outside the chapel, the trio are attacked by gangsters, saying they are looking for someone. They flee and visit Jade, discovering that she is the mother of the baby, whose real name is Tyler, before being arrested by the police for stealing the police cruiser. Having been told that the Mercedes has been impounded, the trio is released when they volunteer to be targets for a taser demonstration, unknowingly. While driving the Mercedes, they discover a naked Chinese guy in the trunk who attacks them and flees. Alan confesses that he drugged their drinks to ensure they had a good night, thinking the drug to be ecstasy.
Returning to their villa, they find Mike Tyson, who orders the trio to return the tiger to his mansion immediately. Stu drugs the tiger with the remaining rohypnol and they drive towards Tyson's home in the Mercedes, but the tiger attacks them, claws Phil on his neck, and damages the car's interior. After pushing the car the rest of the way to the mansion, Tyson shows the trio footage of them at his house to help them locate Doug. While driving, their car is struck by another vehicle intentionally; the passengers are revealed to be the gangsters from the chapel and their boss, Leslie Chow (Ken Jeong) – the naked man from their trunk – who accuses the trio of stealing $80,000 of his money that was in his purse and kidnapping him. As the guys try to deny this, Chow says he has their friend, and threatens to kill him if his money is not returned. Unaware of the location of Chow's $80,000, Alan, with help from Stu and Jade, uses his knowledge of card counting to win $82,400 playing Blackjack.
They meet with Chow and exchange the money, only to find that "Doug" is an African-American drug dealer (nicknamed Black Doug by the trio), who inadvertently sold Alan the roofies. With the wedding occurring in 5 hours, Phil phones Tracy, telling her that they cannot find Doug. After a conversation with "Black Doug" (Mike Epps), Stu realizes where Doug is. The trio travel back to their hotel where they find Doug on the roof, moved there on his mattress while he was asleep, as a practical joke by Stu, Phil and Alan. Doug's mattress had been thrown there by Doug himself, in an attempt to signal for help. Before leaving, Stu makes arrangements to go on a date with Jade the following week. With less than four hours before the wedding and with no flights to L.A. available, the foursome race home, with Doug revealing he has possession of Chow's original $80,000. Despite their late arrival, Doug and Tracy are married and Stu breaks up with Melissa after having grown tired of her controlling his life. As the reception ends, Alan finds Stu's digital camera detailing the events they cannot remember and the four agree to look at the pictures together before deleting the evidence of their exploits.
