Schrödinger places the glass in a box, and informs us it exists in a quantum state of both half empty and half full, but it's actual state cannot be determined until we look inside.

Gary larson's far side gives us 4 personality types:

The glass is half full.

The glass is half empty.

Half full! No, wait, half empty! What was the question again?

Hey! I ordered a cheese burger!

Really it depends on what the glass is full of. If it's water it can go either way depending on the situation. If it's water you're bringing to a man dying of thirst then it's half full. If it's water that is about to be used to waterboard someone it is half empty.

It gets more complicated if it's full of something else. Like baby blood. Then still, if it's going to a baby it's half full, but if it's coming from a baby it's half empty.

Then again you didn't specify what the two halves are. What if the glass is underwater and is half full of sediment. Technically it's still completely full. If it's full of water and is not underwater then the other half is filled with air.

and anyway who cares about the fucking glass. It really doesn't matter one way or another.

To a man adicted to ice the glass is a lemon with a mecheti.

A postal 2 player will kick it with his foot, smoke some catnip, exclaim that he is the lizard king, keep kicking it in bullet-time and go off to use a shovel to behead bystanders who are clapping at your acts of glass-ownage.

Me: Hey, grandpa. Is that mug of coffee half-full or half-empty?
Grandpa: Doesn' matter, it's too hot!
*splash*
Me: Yeearg!

A philosopher would ponder for hours upon how full or empty the glass is and how it would relate to the objects surrounding it.

A Half-Life player knows they put something in it to make you forget. He just doesn't remember.

Chuck Norris says it's full, therefore it is full.

It was so I filled it with water now it tastes funny.

Johnn Johnston:
A lawyer sees only half the opportunites to sue.

Someone already said that...=/

(Can you be specific about the content of the glass?If it's half full of babyblood from a baby, Im pretty sure it's negative) quote from Demetri Martin

It doesn't matter if the glass is half empty or half full, I'm thirsty

Wasn't it originally tomato juice? If so, would that make me a pessimist for seeing it half full? I hate tomato juice.

Besides, in the English language, we say the glass is half full usually. That norm affects the way we think about it and ruins the test.

Who the hell drank from my glass dammit!!

Xhumed:
a smart-arse says: if it was filled, then half removed, its half empty.
if it was empty and filled half way, its half full.

EDIT: Ah damn it, i really need to start reading all the previous posts before i post mine

Yeah that's the exact same thing I was going to say. Which just goes to show there's no such thing as an original thought.
The way I phrase it usually goes:
The current status of the glass is entirely dependent on whether you are filling it up or emptying it.
Then again, I am an engineer >.>

I fill the glass till it is full, drink the water, then leave it on the counter.
A chemist pulls out his microscope and studies the molecules of the water.
A government official wonders how he can screw the water over in order to make more money.

a ninja chicken doesn't care a shit, ninjas don't drink

SeaCalMaster:
A mathematician attempts to prove that a glass must exist.

Shrodinger turns his back on the glass, then muses over whether it still contains liquid

the glass is a lie, wait I think that was taken. Ok the water is a lie. The water is an optical illusion.

I knock it off of the table. Therefore It is now empty. It does not matter what it was but what it is. Empty.

dart sifilis:

A woman talks glass into misery and suicide.

Amen Brother

Esades:
It depends on the direction in which the water was going... If it was being filled, it's half full. If it was being emptied, it's half empty.

This guy has it right.

A chav hopes the glass contains cider, but it doesn't matter anyway because they prefer the bottle.
A man makes a sex joke about it.
An emo writes a poem about how the poor glass feels.

A plumber tries to add taps then overcharges you.
A ninja kills it.
Bruce Lee uses it to beat Chuck Norris to death, without spilling a drop.
Neo runs away before it turns into Agent Smith.
Frodo drops the ring in.
A teenager drinks it then acts drunk.
A model asks for a low fat version.
A twilight fan says how Edward Cullen would fill it with flowers for them.
Orks add rokkit launchaz.
An emo cries because it doesn't love them.

I burn it down :)

I don't know if someone else has said this, I've never heard it before. If there are droplets of water in the top half then half has been drunk or spilled so it is half empty. If the previous condition is not met then it was only filled half way so it's half full.

If people stopped asking silly questions and just drank the damn thing then our world would be a lot happier.

I see the glass of water as meaningless, it's a glass of water and appears to be distracting us from the more important things in life. Do whatever you want with it, and go back to your life. Don't waste time thinking about it's metaphorical meaning.

(What does that make "I"? Been wondering about that.)

A scout adds glykose, sugar and salt to make an enegy drink.
A soldier gives the glass a millitary pepetalk concerning misunderstandings of ancient war strategists.
A pyro mumbles somehing incomprehendable about what appears to be disguised spies before slicing it in half with a fire axe.
A demoman empties it, then fill it up with whiskey, then drink from the bottle
A hwg pulls out his sandwich and exlaims "Why is glass baby size?"
A engineer convinces everybody that the glass is twice the size that it should be, and that he can redesign it to be appropriately sized.
A medic puors it into a pot, boils it and uses it to desinfect his medical equipment.
A sniper slides the glass down the counter, pullse out his rifle, shoots the glass and yells "Spot on!"
A spy disposes of the glass and diguises himself as it.

An old man complains that they had better water or glasses in the good old days.
In communism, either the glass or the water doesn't arrive.
An East German checks the glass for listening devices.
A West German refuses to drink the water, because he claims that it is a socialist drink.
An Alcoholic looks at it for a while, then starts to cry.
A Computer game critic writes a review on the glass, claiming that it's too reflective and that it's bloom is completely unrealistic. Then he writes a review on the water.
A Dictator tries to take it over.
A good diplomat negotiates for glass to be filled. After 8 hours and an impressive amount of arguments, the glass is filled.
A bad diplomat negotiates for the glass to be filled. 8 hours later, the glass is empty and the diplomat is fired.
If you ask someone who is a fan of the movie "A few good men", he shall respond saying "You want Anwsers? You want to know the truth? You can't Handle the truth!"

In my opinion the glass is not full enough, but not quite empty either.

Blake goes to find the where the other glasses are being held.
Orac complains about how the glass is getting more attention than him.
Cally frees it into the ocean.
Gan goes to smash it but his inhibitor chip stops him.
Tarrant goes to shoot it but Soolin already has. And Dayna shoots the pieces.
Vila steals it.
Avon drinks it.
Servalan poisons it.

William Hartnell complains that in his day the glass was full.
Patrick Troughton makes a tune on the rim.
Jon Pertwee convinces it that it is full.
Tom Baker offers it a jelly baby.
Peter Davidson comforts it for being half full.
Colin Baker throws it across the room.
Sylvester Mccoy tries to stop Ace blowing it up.
Paul McGann was too busy.
Christoper Ecclestone thinks it's fantastic.
David Tennant explains that it never was half full because of the unequal spacing of glass molecules; and that it's constantly in motion and how he misses Rose.
Captain Jack tries to seduce it, and succeeds.

And, deep within the shadows, a repeating voice says Drip...drip...drip...

MagnetoHydroDynamics:
A spy disposes of the glass and diguises himself as it.

That would be... difficult.

The Joker tosses the water out of the glass and attempts to drink out of an empty glass, he then proceeds to smack his lips.
A tank pours the water over himself so that the inferior-endurance classes won't get wet
A rapper makes a music video with ridiculous lyrics about it, throws in a few beats, some bitches and a lowrider and makes millions
A Scotsman puts the glass outside for an hour then enjoys a full glass of water
G.W Bush takes the other half from a country with inferior military power
A lolcat says : "I can haz more?" (horrendous i know)

I've got some more but they involve religion and I'd rather not go there even though I don't mean to offend anyone. I think you understand.

Daily Mail Headline - Front Page

'Immigrants claiming up to 50% of taxpayers liquids'

i say there is no glass at all. it is all a government conspiracy to make us discuss this stoopid question whils they are making a clone army of cat-people!!! WHO ARE ZOMBIES!!!!! ZOMBALALALAZIES!!!!!!!

They are coming......

How about the Alcholic Futurist? He sees the glass as halfway to his next beer.