When Brie Marschz (Catherine Keener) and Dana Marschz (Steve Coogan) are arguing in the Mexican restaurant, in the middle of their argument the margarita glass disappears when the camera cuts to Brie and returns when the camera cuts back to Dana.
When the drama students are forbidden to stage their play on school property, they move the show to a warehouse used for raves because promoters won't be using it because they are at Burning Man Festival in Nevada. But the play supposedly takes place near end of traditional school year (May or June) and Burning Man always takes place on Labor Day, in September.
In "Hamlet 2", the play within the movie, Hamlet forgives his father, but Hamlet has nothing for which to forgive his father in Shakespeare's play. If there's anyone Hamlet could forgive it's his father's murderers--Hamlet's mother and uncle. However, although this could be a mistake on Dana Marschz's part, he does prove himself knowledgeable of Hamlet. Otherwise he wouldn't have been able to write a sequel.
After Mr. Marschz trips on acid, the police find him naked from the waist down on an abandoned couch. When he is picked up and escorted to a car, his shirt parts briefly and we can see that he is wearing flesh colored underwear.
Arizona does not issue license plates for the front of cars, though several vehicles are seen with plates on the front.
Dana calls Octavio "Heywood" for much of the film. When he is telling Rand his part in the play is being cut down, he says it was because of "Octavio's performance". Dana does not learn Octavio's real name until later, when he meets with his parents to convince them to let him act in the play.
In the newspaper clipping, "The Price of Free Speech", (38:20) the prose is complete gobbledegook.