Many games offer customisable content, like custom characters and custom stages. Very few games allow you to design a completely new weapon (including it's function) from the ground up. So that's what this is.

What you do is state the name of your weapon, what it does, and what it looks like. Is it thrown? Is it fired? perhaps it's even an air strike type weapon? Thats entirely up to you. A weapon I would create is...

The Kick Button:

Causes the targeted player to be kicked from the game/server.

Appears as a small, hand-held button with a picture of a shoe on, that is thrown at the enemy. Upon contact, the button is pressed, and the player is disconnected.

Okay, my best idea so far is for this sword, but it's not a normal sword. Instead of a blade, it projects a beam of light which can cut through everything except for this one material called "fortosis weave". It's made by getting a magical crystal and shining a giant light through it with a focusing lens. I'm thinking of calling it a "beamsaber" or possibly "lightsword." I don't think anyone's come up with this before. I dunno.

/troll

Edit: Oh, and the point of this post in a meta-sense was to point out that everyone's already thought up pretty much every idea that anyone will come up with, barring those ideas which people make up to be deliberately different in order to prove this point wrong or in an attempt to be viewed as "unique" and "special".

Well, they are "special" I guess. Just not the kind they wanted.

"The Noob Whiner"

A gun so rediculous that every moron with an IQ below bread loaves will cry. (I.E. 3/4 the populace of Xbox live)

An LMG, but it's a shotgun instead of a rifle.

Great for those giant pesky zombie hordes!

A pistol made of wheat.

The most useless weapon ever.

Solely for use as an insult, as in, when you kill someone with it (good luck), you're either ridiculously leet, or they're the opposite.

Or both.

Asday:
A pistol made of wheat.

The most useless weapon ever.

Solely for use as an insult, as in, when you kill someone with it (good luck), you're either ridiculously leet, or they're the opposite.

Or both.

or you're the luckiest S.O.B around and you should go play the lotto.

I feel desperately compelled to mention shurikens and lightning, but I pride my intelligence too much to say it. Oh wait, I just did. Bugger.

My personal best weapon would be a harpoon gun that rips limbs off and pins them to walls. Pinning things to walls makes everything better.

a rocket launcher that shoots dictionaries at people on Xbox live to scare them away because they cant get around the concept of learning.

The Nitrogen Operated Ordnance Ballistic Cannon.

The Lag gun, when you point it at your enemy and fire it causes them to slow down.

The Lag bomb, when you trigger it, it causes a Sauron's-death-explosion-type blast radius, logging everyone out.

Rubber Chicken of Doom, because it would be awesome to kill an opponent by slapping them across the face with a rubber chicken.

A boomerang with a pen-knife sellotaped to it. You throw it just right, it flies around, and stabs the enemy from around a corner. Or, it could go around fortifications and stab them in the back. You could go hunting with it. You could change the channel with it. You could do a helluva lot with it.

Eggo:

the monopoly guy:
An LMG, but it's a shotgun instead of a rifle.

Great for those giant pesky zombie hordes!

Forget that...

hueg

Forget that, you're kinda stuck in one place with that.

Also, my idea is great for taking care of those damn birds tha poop on your car.

So is yours, I guess.

/inb4 "shurikens and lightning"

"The Imcompe-Glock," A pistol with bullets that hamper the enemy's mental capacity, and making them kill themselves in a hilarious fashion.

OverlordSteve:
/inb4 "shurikens and lightning"...

SystemWarrior:
I feel desperately compelled to mention shurikens and lightning...

Too late, mate.

Johnn Johnston:

OverlordSteve:
/inb4 "shurikens and lightning"...

SystemWarrior:
I feel desperately compelled to mention shurikens and lightning...

Too late, mate.

Damn, I wanted to be cool...

a log-cannon would shut some people up, "TIMBER!" "huh?" *smack*

frog launcher would be funny as well

Ooh! stuffed animal mortar

while these are sick and twisted you must admit they'd be fun.

"The Why-didn't-I-Think-of-this Gun"

A gun that when used, upon your next death shows you what you could have done to avoid dying in the firstplace.

"Greedy Bastard"
A gun that shoots money and priceless merchandise to allow a quick escape, or a distraction.

I could think of alot of crazy, wacky weapons, and even simply select one from any game ever made, but i'd never be able to top this:

http://www.youtube.com/watch?v=p4ebtj1jR7c

o_O

...BALLS.

SystemWarrior:
Pinning things to walls makes everything better.

http://liandri.beyondunreal.com/Minigun

Scroll to Stinger Minigun (UT3) and Secondary Fire.

I once pinned someone to a wall. I pinned both his hands, and he looked a bit like Jesus.

(Frozen) Pea Shooter:

Self explanatory.

"Jar of Bees"
Pretty self explanatory. Still want to see it in a game though.

"Octopus Launcher"
Also self explanatory. Launches aquatic invertebrates of any kind at high speeds.

I want a "dog-ear sentry-gun with anti-barry white missiles" This would eliminate me having to mute players all the time because if this picks up a 10 year olds voice or a 12 year old trying to mask his voice it will shoot through walls and cover and the munitions will be coated with voice box cancer and emp's so it will shut them up forever brake their mic and ethernet cable will be destroyed.
Or a chainsaw axe/spear/haleberd.

EDIT:lol, at meatloaf's ideas, i would love to see them in action.

Petroleum Puncher - A crossbow-like device that fired hollow bolts full of propane into the target. A fter a few seconds, a small ingition switch detonates the propane. Ker-splat.

Chainsaw Nuchucks - 'Nuff said.

eggdog14:
I could think of alot of crazy, wacky weapons, and even simply select one from any game ever made, but i'd never be able to top this:

http://www.youtube.com/watch?v=p4ebtj1jR7c

o_O

...BALLS.

I want one. If i were to design a real world weapon.....I would call it the turtle head. It would be a small hand held cannon that emits sound waves that......wait for it........causes your target to immediately poop their pants.

It would be awesome with a automatic-rifle that shoots rounds that sets the enemies on fire and then they would rise again as sexy ninja chicks that aid you by throwing shurikens and lightning at people, oh and of course they would still be on fire.

There, shurikens, lightning, fire and tits :D

AIDS raygun.

A rocket launcher that shoots chainsaws, but instead of blades on the chainsaws, you have miniature nukes coated in acid. Also, it's on fire.

CHARGE TEH LAZUH
SHOOP TEH WHOOP

BFG 9000.6 (POWERED BY AIDS).

HIV+ KNIFE

My dream weapon would be intended for a 3rd person combat-action game such as GoW or DMC. It would be vaguely whip or cable-shaped, long but flexible enough to be controlled by an analog stick. It could target any major limb or other part of an enemy's body including the head and is strong enough to wrap around any selected part and either rip said limb clean off the body if you pull too hard on the stick or send the target flying by that limb into the nearest 10-story drop or wall. One would rotate the analog stick to gain distance through spinning.
If you rip off a limb that is holding a weapon of any kind, it is automatically affixed to the tip until you ditch it. If the limb doesn't have a weapon you can still throw the limb at someone else, including heads. Lastly it would be completely independant of your movement controls, allowing you to spin, rip, or tug while running and jumping around, dragging whatever/whoever you've wrapped up behind you, or even wrap a large creature's legs and weave through them to trip the beast up.

My god, what is up with the shurikens and lightning? Have you no shame?

... and by that I mean have you no shame in ripping off Painkiller? (Hah! You thought I meant Yahtzee. C'mon, admit it!)

I'd go for something useful. I'd love to see Nikita's around, but that's not exactly original. Still, the only game I've played with one is Metal Gear Solid and Ratchet and Clank something, so it'd be great to have it custom made, since few games do it.

Particularly multiplayer. The disadvantage being that you're vulnerable while zoomed in.

"The Fatality Producer"
You fire it at your enemy and upon contact a random Mortal Kombat character appears and uses a fatality on your opponent

As awesome as the above (hopefully) suggestion is, that woulkd require about three analogue sticks. One for character movement, one for camera control, and one for the whip. Unless you're suggesting a Force Unleashed style, wherein the camera or analogue stick is repolaced with whip control.

Un-masturbator! It erases all of your sexual organs if you touch them...you'll be compelled to too.

Killcushley:
"The Fatality Producer"
You fire it at your enemy and upon contact a random Mortal Kombat character appears and uses a fatality on your opponent

FINISH HIM!

chainsaw gun that can control gravity and pulls stuff into its blades