One of my old Dad's favorites sayings was that when he was in the Army, he was so skinny he had to run around in the shower to get wet! Many others he had are unrepeatable here. 
I remember one about so one being so skinny, nobody dared to pull out the bath plug?
Also, my Mum always said when she bathed me that I looked like a "Belsen Baby" - I guess I know where this came from.
Off topic, but I think I must have been the only child in the area who was scrubbed with a scrubbing brush to get rid of the dirt from climbing trees, even after I'd washed off the worst beforehand at my friend's house.