To be told to "Bile yer Heid" or Boil Your Head, is to be told not to be so ridiculous or to be so absurd. Can also be used as a term of exclamation if someone is doing something stupid and its annoying to you. It is a common phrase in old scots but is still used today.
Away n' bile yir head ya stumur, dont be sae stupit! Or 5 grand for THAT, away an bile yer heid!