When Ali G is chained to the fence with his pants pulled down he is seen by a passing group of young school girls. The teacher walks over to confront him and when the camera pans back to Ali G his pants are pulled up. When the teacher is standing in front of him his pants are pulled down again.
When Ali is chained to the fence as part of his protest, Ali can't resist and takes a bite out of a "chicken dipper" that is in the hand of one of the reporters. From the rear of the reporter you see him drop the remaining portion of the chicken into the box, when the view changes to a front-on shot, you see him drop the piece of chicken again.
When Ali is teaching his class, he gives one of the kids two badges, in one shot, they're spread all down his arms, then in the next shot, it is all in one place, then back down the arm again in the next shot.
The number plate on Ali's car "RE59PCT" stands as a legitimate number plate. However this would have been issued between Sept 2009 and Mar 2010. This film came out in 2002.
When Ali G and his friends are dodging the lasers, you can see near the end of the sequence, one of the lasers move slightly.
At the end, when Ali samples a large marijuana joint and exhales for a very long moment, he doesn't quite manage to keep his lips in the exact same position and it becomes obvious the smoke is not really coming out of his mouth but from some device hidden behind him.
When Ali G meets with Borat the camera changes from Ali G to Borat. If you look at the back of Ali G's head, he is darker - clearly somebody else.
The police officer (played by Graham McTavish) that shows Ali G around at customs wears a crown and a pip on his shoulder. This would denote the rank of Chief Superintendent except that the crown and pip are the wrong way round.
During Ali and Ricky's rap in the car at the traffic lights, two background extras across the road can clearly be seen stopping and looking at the filming.
After Ali G and his friends blow open the wall safe, the light bulb used to create the explosion's flash effect is visible behind the safe door.