Picking your kipper

Heard recently in the NW of England, used by an elderly lady in a bank whilst speaking to a member of staff. She had just opened one of the cashier's desks..."watcha been doin', picking your kipper?"

Assumed to imply that the aforementioned lady had been scratching her vagina, or possibly masturbating. Her reply was not documented.....

"watcha been doin', picking your kipper?"