Continuity mistake: When Dale and Brennan are throwing the Christmas presents on their parents bed, the presents on the bed change between the first few shots. (01:00:10)
Revealing mistake: Brennan buries his brother, Dale. When Dale emerges from the ground you can see a blue material burst out as he emerges. (01:06:10)
Continuity mistake: At the Catalina Wine Mixer, Brennan Huff's voice breaks the large glass/ice helicopter sculpture. A few moments later, his step father is clapping and the helicopter sculpture is visible behind him. (01:22:45)
Continuity mistake: When the Billy Joel cover band is performing at the Catalina Wine Mixer, the guitarist is using a Divided by 13 head/cab. This is the green amp located by the drum riser. However, when Dale and Brennan take the stage, the amp has changed to a green Mesa/Boogie Stilleto Ace combo. You can see the Divided by 13 in the shot after the musicians have left, when Robert is explaining how he wanted to be a dinosaur behind Brennan's back, which shows that it wasn't moved by the musicians. (01:23:10 - 01:28:40)
Continuity mistake: When Brennan rubs his nuts on Dale's drums, Dale comes in and starts fighting with him. Brennan doesn't have a chance to put "them" away but in the next shot his zipper is up.
Continuity mistake: When Dale tells Brennan he needs to hear him sing, Brennan has a sword and is swinging it around. After he sings, he gets up and the sword is shown on the floor in its scabbard. They flash to Brennan, then back to Dale and the sword is gone.
Suggested correction: He places it down before sitting on the bed to sing.
Factual error: A video is shown of Derek Huff singing "Ice Ice Baby" at a school talent show that took place when his brother Brennan was 17. Robert states his desire to retire in "in two years," in 2010, making the movie's setting 2008. Brennan is 39 in the film, placing the talent show 22 years ago in 1986. The song "Ice Ice Baby", recorded by Vanilla Ice, came out in the summer of 1990.
Character mistake: When Brennan's brother is talking to Jack in the kitchen, he is holding a Heineken beer. However when he goes out in the tree house and shows the brothers his six pack, he claims he hasn't had a carb since 2000.
Revealing mistake: In the scenes in which Brennan and Dale are fighting with the young children in the park, it is clear that in quite a few shots the children have been replaced with doubles.
Continuity mistake: In the scene where Alice spells words with her food on her dinner plate asking to have sex, the very next view of her shows a smaller plate in front of her.
Revealing mistake: In the dog poo scene, as Brennan is licking the poo, you can see it's a powdered donut.
Factual error: In the film, the Catalina wine festival supposedly takes place on Catalina Island. Yet in a couple of shots you actually see Catalina Island in the background. That's because they are actually at Trump golf course in Rancho Palos Verdes and the island is 26 miles across the sea.
Visible crew/equipment: When Brennan and Dale are talking about the drum set in the living room, you can see a crew member on the glass window.
Continuity mistake: When Brennan and Dale are watching TV, there's a blue can of Pepsi on a table, but in the next shot the blue can disappears from the table.
Visible crew/equipment: When Brennan and Dale are on the stage at the wine mixer, Brennan sings opera and when Dale plays the drums you can see a crewmember reflected underneath the cymbal.
Continuity mistake: In the scene with the bullies, as the bullies are approaching and one says, "Hey, fag stick," Dale and Brennan are stationary next to a tree. When he says,"Long time no see," they are moving to the same position again.
Continuity mistake: When being attacked in the schoolyard, Dale and Brennan are in a different position relative to the big tree whenever the camera angle changes.
Continuity mistake: When Alice writes that she wants Dale to take her now, she places her wedding ring on her plate. However when she and Dale burst into the room the second time, she is wearing her wedding ring again.
Continuity mistake: In the scene where Brennan is showing Dale his sword with Randy Jackson's name on it, his hands switch from having one hand on the hilt to both hands and back when the camera angle cuts to behind Brennan, and back again.
Deliberate mistake: Director Adam McKay states on the commentary that they went to the island Catalina for location searches and realised that he did not really like the island. Instead, on the coast and during several scenes, the island of Catalina can be seen in the background. He chose not to have it digitally edited out as a joke.
