Question: In the beginning of the film, who is the girl in the pink dress who is leaving the trashed hotel room right before the guys wake up from their night, and, why was she sneaking from the room?
Answer: It's Jade, the stripper Stu married. She's sneaking out because she wants to surprise them with coffee.
Question: When they rent the villa for the night Stu pays $4200 for it without any fuss, suggesting money is no problem for him. However, when he finds a receipt for $800 from the casino the day after their wild night, he panics, acting like it's a huge amount. Why did spending $4200 not bother him, but $800 did?
Answer: When they check in, he doesn't actually pay for the villa. As the receptionist said, it was just a copy of the card for security, and they can choose how to pay for the stay upon checkout. At some point in the movie he mentions that his girlfriend checks his credit card statements. This is why he panics at the $800, because she's likely to find it. The copy of the card for the hotel stay does not appear on any statements unless that particular card is used upon checkout.
Question: How did they manage to get inside Mike Tyson's house though they have come in the police car? Can't the security people understand that they are not real police because they don't have badges?
Answer: I don't think the security thought they were policemen. The guys must have broken into the house when there was no security there. When they return the tiger, Mike's bodyguard says they checked the CCTV footage when they noticed the tiger was missing, found the best man's jacket in the tiger cage, and tracked them back to the hotel. There is no mention of any other security personnel except the bodyguard. Even if security guards had seen the police car and assumed they were cops, when the 'policemen' started urinating in the pool and trying to steal the tiger, they would have given themselves away. The guys broke into an empty house.
Question: How does Phil end up in the hospital? They said it was in the pictures but I didn't see anything, just him in the hospital.
Answer: They show Phil in the pictures hanging out the with Carrot Top and getting punched by Wayne Newton; the fight with Wayne landed Phil in the hospital.
Question: Do we ever find out why the Chinese man in the trunk is naked? I understand that Stu claimed he was his lucky charm, but that doesn't explain why he was naked.
Answer: Presumably being locked in the trunk/boot of a car in the sweltering heat might cause someone to get a tad warm whilst in said trunk/boot.
Question: When they realise where Doug is, someone (I can't remember who said it) says, "You can't open hotel room windows in Vegas." Is this true? If so, why not?
Answer: It is true. Its a safety issue. Unfortunately people in Vegas can get a little desperate, and most hotels on the strip are high rises. Someone could lose the rent money or something like that, and jump. Or get drunk and fall out. Most hotels, even in other cities don't have operational windows for safety reasons. I worked for a major strip casino, and we knew of several suicides because of gambling issues, and making the windows non operational helps to eliminate casino/hotel liability. If there are windows you can open, they are usually tiny as to not allow anyone through. Also, its HOT in Vegas, so AC is used most of the time anyway.