When Gord's dad wakes up in Pakistan he has a full beard but minutes later when he and Gord are lay on the desert floor he has a box beard.
When the kid gets hit in the forehead with the bottle, his black eye and other facial injuries briefly disappear, then reappear.
The wreckage of the skateboard ramp in the street changes.
When Davidson throws the cartoons at Gord, Gord drops some, but when Davidson's car pulls away, Gord is holding all of the papers.
The toilet paper in the scuba gear scene changes between shots.
Sexually-abused children or even adults do not go to institutions in real life; their abusers would go to jail/prison. When Gord falsely accuses his father of fingering Freddy. Freddy ends up going to an institution for sexually-abused kids despite being an adult and when the psychiatrist and the cop refused to listen to Freddy and take him away. If the accusations were true, Jim would most likely be arrested and charged; since it's false, Gord would've most likely gotten arrested for making a false report.
Gord could get arrested for impersonating a doctor.
Jim would've gotten arrested for assaulting Darren outside the bank, especially for kicking him in his injured leg.
When Andy (the neighbor boy who keeps getting hurt) tries to chase the limo Gord is in and his father tries to stop him, the blades on the plane start spinning and a pool of blood splatter on the crowd and Andy claims he's OK, but he never would have survived this in real life.
When Gordon gets hit by the bus, a foot falls off the dummy's body.
The "jewels" Gordy gives Betty are obviously just colored glass; they do not refract light in the way real jewels do.
When Gorde's dad gets out of his truck, the cameraman and a few crewmembers are reflected in the side of the truck.
In the restaurant scene, Gord never gives his name to Mr. Davidson, but the man addresses him as Gord despite not yet knowing his name.
Good tells his parents he wants to go to Hollywood to become a famous animator "like Charles Schultz". Charles Schultz was a cartoonist, not an animator.
When Darren is forced to tell Jim where Gord went, he says Gord is in Hollywood selling his cartoons--how does he know that?
Gord would've been easily fired from the cheese sandwich factory for creating a scene and the submarine sandwich shop for creating a scene with a customer.