Deliberate mistake: The car Rudy, the mechanic, is working on is a 1971-72 Plymouth (the one where the chassis falls down around him). Plymouth's of that era were unibodies, which means that the body and the chassis were all one piece and not separate, so there's no way a chassis could have fallen down like that from that particular car, since it didn't have a separate chassis.
Deliberate mistake: The Fremen wear "stillsuits" to conserve their water, yet leave their heads completely uncovered. This would result in quite a bit of water loss through perspiration. (In the book, they wore hoods, masks and nose filters, leaving only the eyes uncovered, but it wouldn't work in a movie to have all the actor's faces obscured!).
Deliberate mistake: As Nancy and her Mum are leaving Rod's funeral, you can see the shot of them leaving the funeral has been sped up. Watch the Volvo "jerk" as it pulls away as the speed is rapidly increased.
Deliberate mistake: When the truck is slamming numerous parked cars on a residential street, it sideswipes a parked Dodge Aspen (white with tan landau top). At the lower-right corner of this shot, a white Chevy Nova is parked at the corner (its vinyl top and trim has been poorly painted the same white as the body). Both these cars are repositioned to be at the roadblock location at the end of the chase, with the Nova slammed from behind by the truck and the Aspen parked near the cop cars. (00:07:00 - 00:07:40)
Deliberate mistake: During the scene with the malfunctioning juice maker, when it goes nuts there is no possible way that all that juice and pulp could have come from just one orange. (00:22:45)
Deliberate mistake: When the geek and the prom queen are driving along in the Rolls-Royce rebel yell scene, the close-up shot of them through the windshield shows a missing rear-view mirror. It was there when the geek pulled out of Jake's garage and it reappears later when the Rolls is parked in front of the house where John Cusack's character lives. This was probably a deliberate mistake by John Hughes so that he could get a better shot of the prom queen feeding birth control pills to Anthony Michael Hall.
Deliberate mistake: In the end sequence, when the joyous Valley of the Wind people run past Yuppa and the old woman to welcome back Nausicaä among the living, the same group(s) of people are seen twice running from the right to the left.
Deliberate mistake: I have participated in several amateur karate tournaments over the years and I have yet to see one that is full contact without any protective equipment whatsoever, especially one in which all of the participants are minors. All of the contestants should at a minimum have had mouth guards, gloves and foot pads.
Deliberate mistake: As David runs from the MPs in the restaurant, he jumps off the balcony onto the bar below. It is very obvious that it's the stunt double for Michael Pare doing the jump. (00:45:35)
Deliberate mistake: Before going on stage in the infamous purple coat for the first time in the movie, the Kid is in his dressing room. The silver jewelry/decoration on his coat is on the left shoulder. In all subsequent shots, the silver jewelry/decoration is on his right shoulder.
Deliberate mistake: The soles of the boots Daisy the cow is wearing have been removed to allow her to walk properly. In some shots, their lack of soles is evident.
Deliberate mistake: Dr. Chandra returns to the Leonov at the end of the film with the device that Dr. Floyd designed to cut HAL's memory circuits. He hands the device back to Dr. Floyd, who tosses it in the air and catches it when it falls back into his hand. One problem - there was no gravity on the ship at the time. (01:44:00)
Deliberate mistake: When Supergirl flies out of the lake upon her arrival to Earth she's wet. When she lands on the shore she's suddenly dry.
Suggested correction: Incorrect. She's not wet when she comes out of the water. She emerges from the water dry in an (incredibly wonky) effects shot. Why she's dry coming out of the water is unclear, but it presumably has something to do with the teleportation process for how she got to Earth considering her costume also suddenly appears on her as well.
Deliberate mistake: At the end of the film, when Alex, Maggie and Grig take off in the Gunstar, the crowd of trailer park residents watching them leave backs into the covered portion of the restaurant, right next to the 'Starfighter' game cabinet, which is readily visible in the shot. Mrs. Rogan then wonders where her younger son, Louis, is. The shot changes to show Louis pulling a bench up to the 'Starfighter' game to play it as dust from the Gunstar liftoff kicks up next to him while he watches it fly. Yet the crowd is nowhere to be seen in the shot of Louis playing the game despite everyone being huddled right next to it on the patio (his mother was standing next to it and should be able to see him). Given the proximity of the crowd to the game a moment earlier, Louis wouldn't be able to play it, let alone put a bench next to it. It's clear the filmmakers chose the image of the younger kid aspiring to be like his brother by playing the game over the logic of where the game was in relation to the crowd.
Deliberate mistake: When Betty walks away from the kissing booth it is clear that she has spike-like heels on her boots. When she steps on to the "moon" surface the spike heels are gone. Her spikes are on up to the point where they enter the room. I am pretty sure the crew did not want to puncture the bladder and have water all over the set. (01:07:25 - 01:09:35)