So you want to know how to eliminate a hostile alien life form from your planet, spaceship, car or foot. How do you go about it? There are many, many ways to deal with such pesky critters and beasties! Your first instinct is most likely to go and grab your double-barrel, good thinking. Although, that isn't always the best way to take care of such a situation. I have just completed my first installment of alternative alien extermination certification course, and I'm going to pass on what I have learned to you!
Remember to stay calm! You're going to want to explore "Alternative ammo". What does that mean? It means anything you can find! I'm going to throw out a few examples for you just to wrap your head around it, and help you think "outside" the box, cocoon, pod or giant gelatinous alien blob thing, whatever you have a run-in with.
The first thing you would probably want for your arsenal of random crap that shouldn't hurt anything at all, is a gun. (Note: it is well noted that this will kill a lot of things.) You want something with enough ammo and stopping power, with a higher rate of fire. If anything else, it would buy you some time. Attempt to secure an AK-47, or more preferably a grenade launcher, failing that, go for a tactical shotgun, failing that try for a .45 cal., failing that, a crowbar would be your next best bet. Now you're strapped, awesome! What to do now? Remember: the gun won't always kill what you shoot at. Most of the time it will kill what you shoot at, then you have some sort of toxic alien blood oozing everywhere, which can be just as bad as that beastie you just executed.
So instead of going right for the bullet to the head method, try going for something a little less obvious. What do you have laying around in your bathroom? A bunch of cleaning products. Perfect! Remember "The Faculty"? Same approach here. Just go ahead and mix up a whole crapload of them, go ahead, I'll wait. When you meet a new person that you suspect is actually an alien bent on dominating mankind (Note: They can be very friendly, keep your guard up.) ask them to try this new wonder drug of yours, if they turn into a screaming melting blob, you've got yourself an alien! Just make sure to pour some bleach on it or something, those can be hell to clean up. Although, it may be a sly alien indeed. Upon refusal to try your human detection drug, you may just shoot them.
Which may lead to: "Wow, that drug is awesome! Got anymore?". Now you're in for it, the alien is onto you, he knows what you're up to. Time to try a new approach. So you're still in your bathroom, just look around! Is there anything else you can use? There sure is. What's that in the shower? Shampoo! Remember "Evolution"? Yeah, supposedly there is a chemical in some shampoo that will leave an alien mutant monster thing writing in a puddle of it's own melted flesh! So what you're going to do instead of "Shoot it in the face!" is grab that bottle of shampoo, pop off the top, and fling as much as you can right into that mean old alien's eyes. Any result? If you're lucky he'll be letting off banshee-like ear shattering screams! If not, his eyes are kinda stingy at best. Well, move on. Or try the shoot it in the face method at this point, if that doesn't work, try this.
Now, beating an alien around with a crowbar or a bat would usually get the job done, not always. Remember "Signs"? He must have cracked every bone in that alien's skull. So you're still cowering in the bathroom crying like a baby, right? Perfect. Grab some sponges, or a washcloth or whatever you have that holds water. Fill it or soak it completely, and now toss your reverse Molotov cocktail at the mean old alien. If it did the trick you should see his flesh melting like a vampire soaked in holy water! The thing is, water isn't everywhere in the universe, sure there is water in most places, what about the guys that don't know it exists? So go ahead, see if the water will be the one thing that saves you! That could only beg the question: Why would aliens come to a planet which is made up of more than 75% of the one thing that could kill them? I'm looking at you, Shamalan. You know what, just shoot it in the face, it would leave a much clearer explanation.
Here's another scenario: Most likely in the event there is an alien invasion, the power would have gone out long before you had any idea. This will most likely happen at night time, as it does in almost every movie ever made involving aliens. Take "Pitch Black" for example. They get stranded on a planet that seems like it will never get dark, and when it does, there are some crazy looking monsters that can't see the light of day, unless they like being dead. So you may be asking yourself how to get some light. Grab a candle and some matches, a flashlight, just shed some light on the situation! If all goes well, then you've got a room full of crumbling critters, congrats! Or you could shoot it in the face. You only have so many bullets though, careful with that ammo Davey Crockett.
These are but a few of the many, many ways to eliminate a hostile alien species that are impervious to bullets. Your options are potentially limitless. Let's say you're on the beach, having a 50's style clam bake with a bunch of your friends. All of a sudden, an alien comes to massacre you and all of your pals. Oh no! Not so fast, there are things near the beach you can use too! Take "Alien Beach Party Massacre" for example, the aliens get bested by sunscreen! I'm assuming the higher the SPF, the deadlier it is to them. Maybe the monster aliens from "Pitch Black" could have used some of that? If that doesn't work, hit it with an oar, or just harpoon it in the face.