I do the picking thing but not eating.
When I was about 13 I picked the skin on the balls of my feet so much, I had to tape cotton wool onto my feet so I could walk to school.
I am also a bugger for pulling strands of hair out, one by one, it is especially satisfying if it is one of those really thick, dark, course ones.
I think it is a mild form of self harm as it causes mild satisfaction / pleasure while doing it,
I pierced my own ears with a sewing needle aged 14, my mum went ballistic!