1. The Plan Kill The Alien - Alien
THE PLAN: After Kane pops an Alien out on the dinner table which then promptly runs off, the crew of the Nostromo realise that they have probably shouldn't ignore it like I ignore the mice in my flat and in fact must track it down and kill it. This doesn't work out too well for poor Brett who gets mauled by the newly massive beast and they can't just abandon ship as there are not enough places in the lifeboat for some hilarious reason, but let's not get into that now. So Dallas decides to jump into the air ducts with a flame thrower and try and drive the Alien toward the air lock where it will eventually be cornered, then they simply blow it out the 'eff out into space.
WHY IT'S STUPID: Going one on one with an Alien is not exactly a great idea for a professionally trained marine, let alone someone who is essentially a miner, so the decision to do this in the environment that 100% favours the Alien is baffling. It's dark, Dallas has absolutely no room for manoeuvre and although he is covered from the rear by the closing of vents, he has no idea what is above or below him thanks to the crappy tracking devices that Ash hastily threw together. Given that they have control over the vents in the air ducts, why not just close them all off? There is a reasonable chance that you would trap it in there somewhere and then you can camp out in the lifeboat for a few days. There is only one entrance to defend so if the Alien makes it's way toward them they will be able to see it coming, not forgetting the tracking devices would give you plenty of warning. Much better than crawling around air shafts waiting to get eaten.