When the Wilsons are picked up at the airport, the dog is referred to as a "he" when the pet carrier is in need of cleaning. Later, at the nightclub, the disguised Marcus Copeland tells Heath to give "her" to him
When the agents hold the Wilsons, thinking they are not the real Wilsons, a tattoo is clearly seen on the lower back on one of the sisters, yet neither of the Copelands when disguised as the Wilsons has a tattoo on the lower back.
When Marcus comes home from work he tells Gina it is only 8:00. Gina then says she called the bar, Marcus and Kevin left at 7:45. She also said that MapQuest said it only takes 6 minutes to get from the bar to their house. Marcus says he got there in 8 minutes which leaves 2 minutes unaccounted for. However, if they left at 7:45 then it would be 7:53 when Marcus came home, not 8. That leaves 7 minutes unaccounted for, not two.
In the bathroom scene, Tori says that she doesn't like Heath for many reasons, one of which is the fact that he drives a BMW 3-Series. However, later in the movie Tori is seen driving a BMW 3-Series convertible.
When the Wilsons' three friends first meet the fake Wilson sisters, the friend with the short red hair is smoking a cigarette. The cigarette disappears in one shot, right before they leave the room. In the very next shot, it's back in her hand.
When Kevin and Marcus check into the hotel as the girls, one of them knocks down the rack of what looks to be pencils. In that shot the counter is full of the pencils, in the next medium shot of them, the counter has only a few pencils whereas the shot after that once again has it full of pencils.
In one shot when the camera is on Kevin (as Tiffany) and his hand is on her arm, in the next shot the camera is on Karen, and his hand is on her shoulder when the camera is back on Marcus, his hand is on her arm again.
During the struggle with the two strippers a lamp can be seen on the table against the wall. But when the stripper is thrown onto the table the lamp is gone. The next shot shows the lamp still missing and an empty electrical outlet, but later the lamp is back and plugged in.
When the thief is being chased down the sidewalk, the agent chasing him is wearing white pantyhose and no shoes. But in one of the shots, the agent can be seen wearing white running shoes with black soles.
In the scene at the hotel when the strippers arrive at the Wilson's door, you can see that Kevin (disguised as Tiffany) is wearing a tan colored pair of slippers. After the action sequence (in which he "protects" himself from the could-be abductors) the camera reveals he is now wearing a blue pair.
At the Hampton reception party, Marcus rushes to the bathroom after eating a dairy product. When he is the stall, his underwear is beige but when Marcus and Kevin go shopping with Karen, Torrie and Lisa, Karen pulls Marcus's underwear up and reveals that it is blue.
When the three girls show up at the agent's door in their pajamas, one of the girls is carrying a stack of magazines. You can see through the peep hole that there's a copy of "Cosmopolitan" on the top. When they enter the hotel room, it's now an issue of "Self".
When Latrell, Tiffany and Brittany are at the club, Latrell drinks his entire glass of apple martini, when the 'girls' hand over the dog, the glass is half full and then switches back to totally empty during the long shot of them all.
When Latrell drives up to the Hamptons Hotel to pick up Marcus as Tiffany Wilson to go on a date, his car is blue. When he pulls up to the restaurant, his car is now silver/gray. Kevin then takes Latrell's car to his mansion to impress Denise. Once they pull up to the house, Latrell's car is once again blue.
In the beginning of the movie, when Marcus is in the back of the car, he pushes a white bag away to talk to the Wilson sisters. When he does, the bag is behind his head, but in the next shot, it's to the right of his face without any time to push the bag away. Also, in the next shot, the bag is behind him again.
When the "girls" are having their sleepover, one of the girls is getting their hair braided. In the first shot we see the head is about 1/5 done, in the very next shot the whole head is done, taking about 5 seconds in real time.
In the scene where "Tiffany" uses the ladies room after eating a dairy product, you can clearly see on the shots of her close up in the bathroom her hosiery and panties are pulled down to her thigh. On shots from outside the bathroom door her panties are just above her ankle. During the scene the position of the hosiery and panties changes.
When Tiffany/Marcus is in the fitting room by himself, his skin color around his butt and thigh area is darker as if he needed more make up touch up. Then when Karen enters to help him with the clothes, his butt skin is very light.
When the Fake Wilsons are shopping and Karen is helping Marcus into his clothes, Marcus says he is size 14. The shot showing the back of Karen before this shows her right pigtail hanging over both sides of her shoulder. The next shot showing her face shows it is all behind her shoulder.
When Kevin and Marcus, dressed as Brittany and Tiffany, leave the dress shop with their friends, Brittany's/Marcus' purse is stolen. When he start chasing the burglar down the street, the high-heeled shoes he is wearing switch from no shoes at all to a pair of white running shoes, then back to the original shoes.
When Kevin and Marcus are in the red BMW convertible with their friends, the front seats of the car are seen to have no headrests. However, when Karen turns around to talk to them, the seats are seen to be equipped with headrests. Also, the layout of the dashboard Tori uses to change the radio station is clearly different to the dashboard seen when Karen is talking to Kevin and Marcus.
When Megan Vandergeld is trying to seduce the designer at the fashion show, he is smoking a long cigarette. When the shot changes, the cigarette that was in his mouth before is by his side in the space of one second.
When Kevin and Denise Porter step inside Latrell's house, the cleaner, "Mei Ling", switches on the lights and Denise's head is suddenly in a different position to where it was before the lights were switched on.
Near the beginning of the movie, they are at a convenience store. There is an ad for Excel gum (with slogan "Excel-erate your breath!" Excel gum is only sold in Canada (where the movie was filmed). However, the movie takes place in New York, USA, where they sell Eclipse gum, instead.
When Agent Vincent Gomez and Agent Jake Harper are searching the Fake Wilson Sisters' room they find the "Wilson sister masks." They should only find one mask because Marcus is on a date with Latrell Spencer.
During the fashion trauma when everyone is fighting: When Russ and "Brittany" were fighting, after Brittany says "My turn" and hits him, causing him to fall into a pile of stacked glasses. You can obviously see that most of them are stuck together, and are fake - judging by the fact that none of them were broken.
When they first decide to go under cover as the girls, they show the make up crew painting their bodies. When the second agent goes into the booth, you can see a little bit of flesh colored paint on the band of his underwear, but this is the first time they are being disguised.
The time of year is summer time, Labor day to be exact. Yet at several times, it appears to be cold. for example, when Latrell picks up Marcus (as Tiffany), at separate occasions they both either breathe heavily or while talking, and you can see their breath as if it is cold outside. Yet the girls went to the beach earlier in the day.
In the night club dance-off , when Marcus and Kevin dance, you can sometimes clearly see that it's not them dancing, and in one shot you can see the black hair of the double popping out of the blonde wig.
The goof item below may give away important plot points.
The cuts on the real Wilson sisters' faces are healed by the end of the movie, when in fact only a weekend had barely gone by. These are the very same injuries that kept them from going to the Hamptons in the first place.