Glass half full? Glass half empty?

I am generally an optimistic type - some might say a "glass half full" person.  But I'm pessimistic about the survival of those metaphors, particularly if pedantic geeks like me get their teeth into them.  Because of course, "glass half full" could equally allude to pessimism.  It depends on whether the glass is in the process of being filled or emptied at the time.  And it depends, too, on what adverbs you might use with the phrase.  All this leads to a list of possibilities:

Glass being filled
Glass only half full: pessimistic - need to wait
Glass already half full: optimistic - not long now
Glass only half empty: optimistic - it was emptier before
Glass still half empty: pessimistic - it's taking ages

Glass being emptied
Glass only half empty: optimistic - still plenty to enjoy
Glass already half empty: pessimistic - oh dear, well, I suppose I was very thirsty 
Glass only half full: pessimistic - I'm sure there was more left than that!
Glass still half full: optimistic- I'm savouring this.

So all this just goes to show...