Northern English slang, meaning "to be covered with shit." This is why the wizard Slartibartfast in THE HITCHHIKERS GUIDE TO THE GALAXY does not want to say his name, and why Arthur Dent laughs when he does.

lil mad is like big mad but the opposite, you mad but not mad to the extent of pullin somthin

To be the fastest bart around (from the hitch hikers guide)