Character mistake: When Charlie is making the come back against the guy in the bar, he only needed twenty but he actually gives 25. When Charlie asks how many so far a guy yells out 14, but he's actually at 19 at that point.
Character mistake: When Hollywood Montrose tells Jonathan Switcher that all the female mannequins have been stolen, they both run into the front window where there's a female mannequin.
Character mistake: During the scene in the diner, there is a sign that reads "EMPLOYEE'S ONLY." There shouldn't be an apostrophe.
Character mistake: After Ricky has just killed his girlfriend with the car antenna, he's challenged by a police officer. Officers would never walk right up to someone who have just committed a murder. Police would always order the suspect into a position that presents the least amount of threat and minimal chance of resistance. Grabbing the officer's gun would never had been an option.
Character mistake: In the final scene of the film where Axel is leaving, and Taggart says "See you around." when Axel turns around to start driving he says "Be cool Rein..." He accidentally uses the surname of the actor, Judge Reinhold, who plays Billy Rosewood. However he cleverly tries to cover it up by trailing off his sentence as he knows he has made the mistake. (01:34:15)
Suggested correction: He doesn't say "Rein", he says "be cool, man." But that was the end of his sentence, he wasn't trailing off.
Character mistake: It doesn't occur to our heroes (admittedly kids) that you don't need to understand German at all in order to read it out loud. It's arguably easier to read than English! The only inscrutable letter would be "ẞ" but Scary German Guy's right there for help. (True, this is essentially what they end up doing in the end, but they still come about it through a "you don't need to be of age to be a virgin" realization rather than the even simpler "you don't need to know German.").
Character mistake: When Modoc is suggesting what type of blood to drink, he suggests pigs blood B-. Swine don't have B blood. They have A and O blood only.