When Paul gets pizza, flowers and a movie, we see him getting the pizza first. As he picks up the pizza box, he has a plastic green bag in his hand (presumably containing the video), but next we see Paul at the video store, where he is pizza-less. He rents a video, which is put into a green bag and given to him. (This makes sense, since he would probably get the pizza last so it would be hot.)
When Paul is approached by Noah who shows him the party drugs, Paul pretends to put them back in Noah's pocket to hide them from onlookers. Instead of doing so he goes to hide them up his sleeve so he can throw them away. When Noah leaves, he pulls the drugs from out of his sleeve. But before this, when he does the motion to put the drugs up his sleeve, his hand is clearly empty-with no sign of the drugs.
When Dora and Paul are sneaking in to the second act of a show with the smokers, they are seen watching the song "Willkommen" from the show "Cabaret". The song "Willkommen" is the very start of the show, welcoming the viewers to the Cabaret, and would not be seen at the beginning of act two.
Though they were supposedly born during the course of Paul and Dora's outing, the kittens they find when they return to the animal hospital are clearly at least six weeks old. They have long hair, their eyes are open, and they are able to move around very well on their own. True newborn kittens are basically helpless.
The age of consent in New York is 17, not 18, as stated in the movie. College students in New York would know this. Even if they didn't, Alcott would not be in prison, and the end narration would not say he was.
Though this was probably done for our benefit, while Dora is running for the "11:50" train, we hear a voice over the P.A. system say that particular train is leaving and from what track it's leaving from. Announcement are not made for departing trains in Grand Central Station.
After seeing the musical "Cabaret", Dora sings "The Best Things in Life are Free". The song is clearly meant to be her rendition of a song from the musical, but this song has never been featured in "Cabaret". The song from the musical is actually "Tomorrow Belongs to Me".
When Alcott says, "If Betty Friedan were alive...," this was meant sarcastically. He's probably well aware that she was alive when the movie is set.
While some have claimed that the fountain in Washington Square Park is only on during the summer (contrary to the fall and winter shots), an NYU student has confirmed that it also runs during the school year.
Near the start of the film, when Dora rushes to catch the "11:50" train, the station clock clearly reads 9:59.
When two of the guys that Paul shares a room with, about half an hour into the film, argue about whether a girl with a pierced tongue is a lesbian, one of them calls the other one "genius" sarcastically... but his lips are clearly saying "idiot".
In the scene where Adam, Chis and Noah are walking down the street talking about how to "Resolve this Paul issue," Noah says "I mean I try to get along with everybody but that guy's got no personality." His lip movement doesn't match up with the audio at the end of the sentence.
In the laundry room scene between Paul and Chris, Chris pranks Paul by grilling him about whether he was sleeping with his girlfriend. After fessing up to the prank, Chris says, "I'm just playing with you," but his lips are clearly saying, "I'm just fucking with you" (presumably to retain the PG-13 rating as there is another F-word mention later in the film).
The subways used in this movie are clearly not New York City subways. The subways in New York do not have padded seats or rounded windows.
Toronto buildings are seen in "New York" throughout the movie. (e.g. when Paul and Dora are walking on the street at night, they walk past Lee's Palace, a concert hall on Bloor St.)
Nobody mentions or even seems to notice the six-pack of beer that sits on Paul's lap throughout his meeting with Jay and his roommates.
At the hospital, Paul is capable of giving Dora Diamond's full name to the doctor. But he was told Dora's first name only by her a few hours before, when he invited her to the Everclear concert. He's not supposed to know her last name at this moment.
Although Dora may have simply been lying, Rubin Hall is in fact not an all-girls dorm, but rather is a co-ed dorm like every other NYU residence hall. Presumably Paul would know this. (There's also mention of a fictitious Hunt's Hall, but this is allowable.)
Dora convinces her obviously over-protective mother that she is spending the night with a friend in the "all-girl's dorm." Later, she basically moves in with her professor-boyfriend for what seems like several nights without even a thought of what to tell her mother.
Misspelled "Financial Aid" in summation before credits. (Corrected for the television version.)