The Glass is Half Negative

It is widely accepted that the positive way to indicate that a glass is at 50% capacity is to state, "My glass is half full." The negative being to say, "My glass is half empty." But what do you say when your glass is at 50% capacity of something negative?

Would it be positive to say, "My glass is half full of poison?" Or would it be negative. I suppose that depends on whether you have already ingested the other half! But supposing you had not drunk half a glass of poison and you were now sitting before the glass that was at 50% capacity with hemlock would it be more positive to say, "My glass is half full!" or, "My glass is half empty!"

Ok, let us say that it was not poison, or anything that could kill you, but rather something that you truly did not wish to drink. Let us imagine that your daughter has spent the last hour conjuring up a pot of hot cocoa, but by some mishap she has laden it with four times the salt required. It will not kill you to drink it, but it will pain you. At such a time it would be more positive to say, turning to your wife who has not managed to drink as much as you, "My glass is half empty!"

Anyway, my car ran a little hot yesterday so this morning I opened the radiator cap and found that the radiator was half empty of mud! I'm trying to be positive about this, but something tells me this is very bad.