Visible crew/equipment: In the scene where Joe goes to Buffalo Bob's house, as he is pulling up to the house you can see the shadow of the camera man in the passenger's seat.
Continuity mistake: In the oil well scene during the fight, Joes coveralls have a bright clean patch on the back, but when the bad guy throws him to the ground the patch is dirty, a few seconds later as he kisses the girl and shares his skoal with her the patch is clean and bright again.
Plot hole: The scenes involving Kickin' Wing, Clem, and the radio station are supposed to be years apart. When Joe is driving to the Hall of records, Kickin' Wing states that the incident was "more than ten years ago." Joe was abandoned in 1979, meaning this scene takes place between 1989 and 1993. In the scene where Joe denies that he saved the kids (from the gas), he refers to the incident as "15 years ago" meaning the scene takes place in 1994. By the time he gets to telling his story on the radio, it is 2001, and curiously, Joe never seems to age at all in between that time.
Revealing mistake: In the scene where Joe talks to the mean parking guy and then speeds away spinning his tyres, If you look at the pavement there is already a mark where the car had burned the tyres. The shot had been tried once before, leaving almost identical marks from his tyres.
Factual error: At the end when Joe, Brandy, Clem and Charlene, the alligator woman are in Joe's 1967 Plymouth GTX, Robby claims his car is faster. Charlene chides back about his Trans Am, saying 'you think you can match that little old slant six against his 426 Hemi?" Pontiac Trans-Am's did not come with slant sixes, a Dodge motor. His was obviously a V-8, and would have most likely have been a 400, but we get the 'yours is really small' reference.
Continuity mistake: At the end of the film as Joe and "family" are getting into the convertible, Christopher Walkens' character starts to get into the car and has one leg fully into the car, the next shot shows him still a few feet from the car and starting to lift his leg into the car.
Factual error: When Joe is at the dealership talking about the Rambler, the dealer says they came with a 289 automatic with 3 on the tree. It is impossible to have both an automatic transmission and a "3 on the tree" which is a manual transmission, at the same time.
Revealing mistake: When Joe is on the bridge and about to jump, the cop ropes him with a bungee cord. It's a single-stranded cord with a loop like a lasso. When Joe falls, however, it is a multi-stranded bungee cord with a proper ankle wrap. Obviously, it wouldn't be safe if the stunt man jumped with just a lasso, but it's obvious that it's two totally different ropes.
Factual error: In the scene where Joe Dirt is talking to the sales rep at the dealership about who ordered the Rambler wagon, the sales rep mentions it came with a 258 cubic inch engine. No Rambler ever came with the 258 six. American Motors (makers of the Rambler line) came out with the 258 in 1971, 2 years after the last car with the Rambler name (the Rambler American), was sold in 1969. Although I was impressed that they bothered to mention an actual American Motors engine, it's still not correct.
Continuity mistake: When dealership guy says the best he can do is give Joe a print out, his hands never touch any keys to start printing the document. (01:01:35)
Visible crew/equipment: When Joe is having sex with the girl after she says she is not his sister, there is an outside shot of the shack shaking with a lamp rocking back and forth. If you look carefully, you can see the filament used to make the lamp move.
Continuity mistake: Seen from the hot air balloon, the passing airplane is a 747. In the close-ups of the cockpit, the plane is a Convair 880, as seen by the distinctive window arrangement.
Continuity mistake: The Indian's braids change length and density from his initial meeting with Joe to later scenes.
Continuity mistake: When Joe arrives at the old house, both his hands are on the gate. Then when you see Joe again from the sidewalk, his left hand is not touching the gate anymore. (01:05:30)