Alternative to "nigger". As where "nigger" can make you sound like a racist and get plasticpants action, "digger" is more witty and sly. Note how both words rhyme.
Someone who feels compelled to dig at and play with their own feces, before and after it has left the body. May be linked to coprophilia, but more often the term is used by geriatric care workers and is simply attributed to dementia.