While in the arcade, Sophie's ski-ball score constantly changes.
Gavin receives a wedgie towards the end of the film so violent it rips what appears to be white briefs off of him completely. However, a short time later, the top of Gavin's boxers are clearly visible.
Sophie's arm changes position when she is first fighting Gavin. It is up then it is suddenly down.
When Zerk is dropping the Sasquatch turd in the forest there is a long shot where Gavin and the gang are approaching in the distance. It pans over to Zerk and Shirts who are standing so close together that Zerk is able to strike Shirts with his hand. A split second later in the next shot, Zerk and Shirts are standing several feet apart with too much distance between them for Zerk to have struck Shirts.
Obvious cast of the dung, since the big kid hit the dung, and it stayed the same shape. This is actually not what happened in the scene at approximately 7:10 Hobie trips and falls landing on his right shoulder just in front of the big pile of poo. He rolls forward with his face toward the ground, lifts his head a bit showing the pile of poo on the ground behind him. He has no poo in his hair or the right side of his cheek. If he had actually landed on the poo that would have left open a lot more crass jokes for the teenage boys to make. No jokes no poo on the face. (However, it still could be and probably is a fake pile of Sasquatch poo.
When Zerk is shooting at the range (about 17 min. in) the hammer of the revolver he is using never moves while he is firing which means the muzzle flashes were added later.
In the "Laser Barn" when Shane and Gavin are the only ones left, toward the bottom of the screen a microphone is clearly visible.