Britney's single 'Oops I did it again' was released mainstream in 2000, and given the hiatus of six years between the prequel and this movie, 'Bride of Chucky' 1998 and this in 2004, there is therefore no way Chucky would have known that song let alone the lyric, as he was not 'alive' in 2000, only resurrected in 2004.
When Glen/Glenda cuts off Chuckie's head with the axe you can clearly see it roll all the way to the right but when they do a close up of it later the head is positioned as if it had rolled to the left.
In the beginning of the movie when Glen/Glenda goes to the little girls room, he goes and stabs the doll. You don't hear a knife being removed from the dolls head and when he looks at the little girl and then looks at himself wetting his pants, the knife is in his hand again.
When Redman get killed by Tiffany, the bowel of Redman are lying on the floor an are smoking. But they can't smoke because bowel got body-temperate 37°C and so they can't smoke because they aren't hot an the room isn't that cold.
When Tiffany is reading the 12 steps to addiction book, when the book is facing away, she's reading the page on the right. When we see the book, she's reading the page on the left. Furthermore, she skips to step 9, which is on the page after steps 1 and 2, but the title for step 9 is on the left page at the top when we see it.
When Glen/Glenda is speaking to his parents in Japanese he calls them otoosan and okaasan which is used to identify another persons father and mother. He should use chichi and haha which are used to identify your own parents.
The prop dolls are shown with large plugs with wires coming out of each of their backs, however when the tech removes the back plate from Tiffany's back (Which is completely exposed) there is no sign of anyplace where a plug would be present.
The goof items below may give away important plot points.
In the scene where Chucky and Tiffany kill Tony Gardner, Chucky and Tiffany get splattered with blood. In the next scene with them in it, they are clean and Tiffany's dress is spotless. She was wearing a white dress, which is really hard to get blood stains out of.
The sulfuric acid in the paparazzo's office is made out to be concentrated sulfuric acid (due to the damage it caused in the murder scene). However, for photography purposes, the concentration of sulfuric acid required is not high enough to cause the immediate damage that we see. It would take about two to three minutes to cause any severe burns to the skin using dilute acid.
After Chucky hits Tiffany in the face with the axe and she falls down on her back, there is currently no blood on her face. In the next shot, she is shown with blood down her face instead of off to the side. The blood on her face would only be possible had she been at a vertical base.