When Heroin Bob is in the doctor's office getting his hand examined, his ring is on his middle finger, but on the X-ray (visible behind him) it is on his ring finger.
The sun on Stevo's face during the conversation with his father in the car.
In the music credits for a Ramones song, the first name of Jeffrey Hyman (Joey Ramone) is misspelled as "Jeffrev."
When Heroin Bob is talking to Stevo while he lies on the ground with his head resting on a block, Stevo wears sunglasses from the camera angle view from the sky. It then focuses on Heroin Bob talking, then when the focus is back on Stevo, his sunglasses have disappeared.
When Mike slams the kid into the wall at the party where Stevo is introducing the characters, the wall bends slightly--but visibly.
When Stevo and the punks jump the neo-Nazis at night, Heroin Bob's bat is obviously made of rubber as it bends on the back of a neo-Nazi.
After Stevo yells at the kid with the Union Jack patch, the kid walks off in the background and his jacket has the Operation Ivy logo on it--a band that was formed in 1987. The movie takes place in 1985.
At Mark's house, Stevo is wearing a shirt with the cover of Naked Raygun's "Raygun... Naked Raygun" album on it. Naked Raygun was a band in 1985, but "Raygun... Naked Raygun" was their last album, and would not be released until 1990.
In the Wyoming liquor store, a Domino's Pizza ad on the wall features their 1990s logo; the film is set in the mid-1980s, when Domino's still used a logo that was all capital letters; this is clearly the then-modern lowercase-letters one).
In the flashback at the end of the film that can be deduced to take place no later than 1976, Steveo and Heroin Bob are ready to play a version of Dungeons & Dragons that didn't exist in 1976. The song playing in the background is "The Trees," which is on Rush's 1978 "Hemispheres" album.
In the shot of the city in Wyoming, there is a modern Best Western sign.
Mark's gun does not make the same sound as a regular .44 would when firing.
In the scene involving the school cop chasing Sean across the football field, the tire marks from the camera trolley can be seen behind the actors.
When Steve-O is talking to his father in the Porsche, a cameraman wearing a striped shirt is visible in the reflection of the car door from the left-hand side.
A light is visible in the backseat of the car as the characters get out and walk toward the liquor store in Wyoming.
When Stevo and his friends are shown driving to Wyoming, they're actually driving west on Interstate 80 toward Nevada.
When Stevo is introducing people at the party, he introduces Jennifer and says "She's got this brother, his name's Chris. He's this death-rock, punk guy..." and when Chris is introduced later in the film, Stevo hugs him and describes him as a "total hippie".