On a train recently, DS picked up a mostly drunk bottle of Coke and wanted to drink it. I was not getting anywhere saying 'yuck, it's rubbish' cos he was just mimicking my words...until I had a flash of genius and told him it was 'dirty water, just look at it'...no more asking to drink it, just happy to roll it on the floor of the carriage the rest of the way home! Probably not that shameful, as I wouldn't mind if he considered it dirty water for the rest of his life...