Someone left a cake out in the rain ...

well, an unfinished drink. Like the careless relationship in  MacArthur Park
someone has left their blue drink out in the Dumbarton Road rain. They will never have that recipe, or taste again.
Did they have to dash off for a dalliance? Was this the drink they carried out of their early morning nightclub until they realised that they'd had enough? Maybe they were simply leaving it out long enough for a weather refill. They won't be waiting long. 

mmmmmm.. rainwater cocktail .... care for a sip?