Just to be pedantic for a moment and to allow myself the immense pleasure of perhaps correcting Mr T, should the expression not be "To lye like a pig in shit".....This expression was often used in reference to slovenly or lazy individuals in rural Scotland.

Strangely enough I had a labourer once who had worked most of his life as a swineherd.......he used to get angry at this expression saying....."Pigs ur no' durty animals, thur beds ur as clean as yer ain".... :0)