No effects or prosthetics were created for Stu's missing tooth. Ed Helms never had an adult incisor grow, and his fake incisor was taken out for the parts of filming where Stu's tooth is missing.

Mike Tyson revealed that he appeared in the film to fund his drug habit, and that he was high on cocaine when he filmed his scenes. Tyson later said that working on the film convinced him to change his lifestyle.

Ken Jeong's wife Tran was battling breast cancer and undergoing chemotherapy treatment, which was difficult for the family as Ken was shooting the film in Las Vegas. Bradley Cooper drove Ken to Los Angeles so he could be there for his wife. Cooper invited the couple to spend the holidays with him and his family. Ken said, "It got me through the most difficult period of my life." Tran was declared cancer-free after the film wrapped.

Ed Helms' and Zach Galifianakis' songs ("Stu's Song" and "Three Best Friends", respectively) were improvised.

When the cop car pulls up in front of Caesar's Palace, two real employees are having an argument in the background about the filming of the movie.

Continuity

In the opening scene where Phil is talking to Doug's fianc?e, the scratch on his lip is perfectly visible. When they show that same scene later on in the movie, Phil's scratch is still visible, and Stu and Alan are still dirty from the day before. However, the night before, they had cleaned up for the blackjack scene, and none of their facial flaws were able to be seen.

When the Chinese run into the side of the Mercedes, there's no evidence of damage on the SUV when they back up and then get out to confront the guys about the money.

When the tiger wakes up while the guys are driving through the tunnel, there's a chain on its neck which disappears between shots.

Alan admits he slipped a roofie into each of the shots taken on the roof of the casino. However, in that scene, he hands each of the other characters an empty shot glass and pours while they hold them. It would be extremely unlikely that none of the other guys wouldn't notice a pill in the glass already or Alan dropping one in each after pouring. The only possible explanation for this is that Alan put four roofies in the bottle of Jager before handing out the glasses, but doesn't seem likely since he says it was one hit each. Four hits in a full bottle would make individual shots more dilute than a full hit per shot.

The damage to the car keeps changing during the movie.



Factual errors

In the police station when Alan is "zapped" in the face he opens his mouth and starts to gasp in pain. Electric shocks tighten your muscles so he would be unable to open his mouth to speak or gasp.

There is far more than $82,000 in chips in front of Alan at the blackjack table. Even factoring in Stu's initial investment and hotel fees there should be much more than that left.

When Alan is counting cards, he is quite visibly mouthing the numbers as the cards come by. While he was indeed eventually spotted by security, that was $80,000 and hours later. If there is ANY indication that someone is counting cards in a casino, they would immediately be escorted out.

The tiger scratch marks on Phil's neck are too small to have come from a tiger, whose average paw width is 4? inches.

The guys go to a hospital and the doctor they are talking to is performing a physical exam. This would be a gross violation of confidentiality and the doctor could lose his license for doing this. In addition, a doctor would be very unlikely to perform a physical exam in a hospital. This would usually be done in a clinic.



Incorrectly regarded as goofs

The formal name for "roofies" is given as "Ruphylin". The drug is really a trademark brand named Rohypnol, but was changed for the movie because the makers did not want to be associated with the depicted criminal activities.

Mr. Chow, at one point says "Suck on these little Chinese nuts", but speaks Korean to his "goons" when commanding them to remove the main characters from the car. Mr. Chow never calls himself Chinese, the previous statement could have been his attempt at humor (He is always making jokes and laughing.) Chow is a Chinese last name and it is entirely possible for someone that is Chinese to be able to speak Korean as well.

Phil, Stu, and Alan are able to obtain the Mercedes from the impound. A car cannot be released from an impound without showing proof of ownership, which they did not have because the car was not theirs. However, while normally this is the case, the fact that they were released "off the books" provides a completely reasonable (or at least internally consistent) explanation for getting the car back without any red tape.

Although the guys supposedly have no memory of the night before, they are still able to go back to Mike Tyson's house, even though he never gives them his address. However, it's not difficult to find out where a celebrity lives in Las Vegas.

The Chinese violently ram the side of the guy's car with their SUV, but when they meet again the next day in the desert, there is no damage to the front end of the SUV. However, Mr. Chow is obviously a wealthy man and likely has more than one SUV.



Revealing mistakes

Mike Tyson explains to the guys that he found out who they were and where they were because Doug left his coat in the tiger's cage, but later on when they are watching the security tapes at Mike Tyson's house, you can see Doug wearing his coat as they put the tiger in the back of the cop car.

When they are preparing the steak for the tiger it is very soft and floppy, Allan is even able to fold it in half. However, when Stu takes the steak to be fed to the tiger it is very stiff, indicating that it is a prop.

When Eddy brings out the "Highroller Package" that was ordered, the picture of Stu and Jade is in broad daylight. Jade had said the wedding was at about "1". The valet ticket that Alan finds also says they were back at the hotel by 5:15am, before the sun would have even risen.

The baby "Tyler" is a different baby from shot to shot. The first baby has very distinct eyes. Later when Jade takes Tyler you can notice it is a completely different baby.

When Mr. Chow jumps out of the trunk with a crowbar and starts hitting Stu, Alan and Phil, the crowbar is a prop obviously made out of rubber. Also, when Chow hits Stu with the crowbar, the crowbar bends.



Miscellaneous

Chow tells the gang to meet him at 'big rock in Mojave desert'. There does not appear to be any distinctive big rock near the meeting spot.

The doctor tells Phil that a large amount of roofies were found in his system even though Alan had only slipped one hit into each of the guys' drinks.



Audio/visual unsynchronized

When Alan accidentally hits baby Carlos with the police car door and he starts crying, you can really tell that baby Carlos was not really crying.



Crew or equipment visible

When the guys push the car to Mike Tyson's house, lighting equipment, the camera and crew members are reflected on the side of the car

During the scene with Mike Tyson, you can see the reflection of the crew and equipment in Phil's sunglasses.

As the stolen cop car drives up onto the Vegas sidewalk, you can clearly see the camera crew from the reflection in the marble building as they dolly along with the car.

During the first fight with the Chinese guys the camera crew can easily be seen in the reflection of the bus stop in the background.



Errors in geography

While driving to Vegas, the background continues to jump around to various spots on Interstate 210 in Inland Empire, CA, then quickly jumps to them driving on Interstate 15 past Barstow, CA. (about 100 miles away). Similar occurrences happen on the way back from Vegas.

Towards the beginning of the film, when Alan makes the mistake of saying "ri-tard" instead of "retard", it appears that Doug is driving in the middle lane, as a car passes them on the left. However, in the long-shot where we see the car snaking up to the camera, it is obvious that it's only a two-line road.

While driving to Las Vegas we see that the guys are on the 210 west. To get to Vegas you then have to take the 15 north in the Rancho Cucamonga area. However there is a moment while on the 210 where you can briefly see a road sign for the Riverside Ave exit in San Bernardino. This means they overshot the 15 freeway by several miles.



Plot holes

Doug, Alan, Phil, and Stu go to Vegas on Friday (evidenced by Phil saying "It's the weekend. You don't know me, and I don't know you" or something similar to one of his students after school lets out). The next day, presumably Saturday, they are hit with tasers as a demo to a group of schoolchildren on a field trip.

Stu is able to convince Melissa that he is wine touring out in the country instead of in Vegas. He says that the hotel that he's in has no phone or TV. If Melissa is "like a forensic accountant" (and therefore probably smart enough to see through a lie if there is a loose end), how would he explain the near-perfect cell phone reception?



Boom mic visible

During the scene in the convenience store, right after the clerk gives the total for the purchase, a boom mic can be seen at the top of the screen for about half a second.



Character error

When the doctor tells the trio (Phil, Stu, and Alan) that Doug's blood work had come back, he tells them that Doug had a large amount of a drug called Ruphylin in his system. He then clarifies by saying "Ruphylin... roofies. Commonly known as the date-rape drug." Ruphylin is a euphemism for Rohypnol (whose makers would not want its name associated with the criminal activity depicted in the film), but a doctor looking at a blood work report would have likely referred to it by its generic name, flunitrazepam, or by its drug class, benzodiazepine.

When the 3 main characters and the baby go down to get their car (which subsequently is the police cruiser) from valet and are opening the door to get inside, the back door is opened for Alan and hits the baby, Stu says to Alan "you just nailed the baby" and clearly blames him for being the one to hit the baby with the car door, however, you can clearly see that Stu was actually the one who opened the door and hit the baby. Stu opened the door for Alan because he was using both hands to hold the sunglasses up to the baby's face.

The physician's physical examination of the elderly patient is nonsensical: practitioners are taught to examine one bodily function/organ or "system" after another, not randomly as it is portrayed here.

When Phil asks Doug if Alan is "all there mentally", Doug tells him that Alan is just an odd guy but that Tracy had said not to let Alan drink too much or gamble. Phil then compares Alan to a Gremlin since he "comes with instructions". In the "Gremlins" franchise, the rules referenced apply to Mogwai and if those rules are broken, the Mogwai then turn into gremlins.