Stupidity: Lao Che's intention was to kill Indy. He had no intention of giving him the antidote. So then why would he bring a real antidote? Why not just fill it with something else instead? From his perspective, bringing a real antidote was a waste of time, and also very stupid in case Indy managed to get it, which he did. In fact, Lao Che could've brought a fake antidote and given it to Indy. He probably wouldn't have noticed the difference, and then there wouldn't have been a fight in which one of his men was killed.
Suggested correction: If you're using a poison it is always worth having an antidote nearby just in case something goes wrong.
Lao Che could still have the real antidote in his pocket and give a vial a fake antidote to Indy. Plus, if you're implying Lao Che would need the antidote should he accidentally be poisoned, it would also be a stupidity for him to give the antidote to Indy.
Lao Che's goal is not to kill Indy, it is to get the emperor's remains without having to give up the diamond. He even tries paying for the emperor outright with valuable coins. He brings the antidote in case he loses track of the poisoned glass and the wrong person is poisoned. He never intends to actually give the antidote to Indy, he's only using it as leverage so Indy will hand over the diamond without making a scene. Indy only gets the antidote after he kills Lao's henchman and the antidote is knocked off the table.
Stupidity: When the parents knew Freddy was doing the killing then why didn't they watch him like a neighborhood watch so they could catch him trying it again, and thus avoid the legal technicality which threw out of the first case? It seems idiotic they broke the law to punish this lawbreaker.
Suggested correction: The parents believed Freddy would not face justice for his crimes. They were unwilling to allow him the opportunity to kill another child, and believing the justice system had failed them they took the law into their own hands. They completely got away with their vigilante justice. The only bad thing that happened was Freddy was brought back as a vengeful demon with superpowers. There is no way the parents could have known this would happen.
It is still a stupidity. Even if they wanted him to suffer, they would try to avoid legal problems at all costs. It is good that they wanted to prevent him from killing another child but they still shouldn't act so hastily.
Stupidity entries are not meant to be stupid acts by characters. They're for minor plot holes. Without in-film evidence why the acts would be a plot hole, there is no stupidity mistake. And assuming what characters would or would not do does not make a valid mistake (not to mention revenge killings do happen in real life and in movies a lot).
No, it's not. What else were they supposed to do when he was caught and set free? It's still not their fault what happened next.
Stupidity: Despite being assaulted by an intruder that she managed to temporarily fend off, the female neighbor takes forever to say something when she calls the police, which is just enough time for the villain to regain his senses and attack her with a huge drill.
Stupidity: It's mostly a fun absurdity, but it is somewhat contradictory to showcase the Ghostbusters being featured as the cover story of every major publication and news outlet, and yet to get help not only they put an ad on the newspaper, but a single person applies for the job (which is all it took for them to accept).
Stupidity: If the ninja can inhabit a dead body (and one that has been dead for a LONG time, even) without any penalty in his agility and powers and it is stated that only another ninja can truly kill him (which surely seems correct, since he would still fight even when hit by hundreds of bullets), the whole movie plot that involves him possessing Christie - who is a reluctant and part-time host - does not quite make sense.