Well? 
Full. 1/2 water + 1/2 air = Full.
Yes. 
If your intent is to drink a full glass of water, and you drink half of it, it is half empty. Since the intent is to empty the glass.
The glass is twice as large as it needs to be.
The issue is water, who cares about glass?
If someone is filling it and has stopped temporarily it is half full. If it has already been filled and someone is in the process of draining it, it is half empty.
just fill it up with plenty of ice cubes.
There are, it has been said, two types of people in the world. There are those who, when presented with a glass that is exactly half full, say: this glass is half full. And then there are those who say: this glass is half empty. The world belongs, however, to those who can look at the glass and say: What’s up with this glass? Excuse me? Excuse me? This is my glass? I don’t think so. My glass was full! And it was a bigger glass!
– (Terry Pratchett, The Truth)
Half-empty.
And the part that’s left is probably poisoned.
I dunno how full it is, but there is always a tiny little chip in the glass right where I drink.
Hey, I wanted wine, not water.
half full. Even when its 1/8th full I always say ‘the glass is only 1/8th full’
It’s half a glass of water. If it was a recipe that called for half a cup of water it would be irrelevant. Same here. It’s absolute, and non-judgemental.
It is holding 50% of its rated capacity.
It’s not what I ordered at all.
But seriously? Depends. If the last thing done to it was to add liquid, it’s half full. If the last thing done was to remove liquid (by drinking for instance) it’s half empty.
The glass just wants you to THINK it’s half full.
Probably more. Do you fill glasses up to the rim?
If is is beer, it is half empty.
If it is soy milk, it is brimming half full.
::Drinks the water::
Empty!
::Gets up and refills the glass.::
Wait, this isn’t a game thread? Oh, ok then.
::Drinks half the water in the glass, sets it down, and leaves. On the way out, he is almost flatten by a giant squid going past.::