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.
"You've stepped in dog's muck and gotten your shoes and clothes all slarty."
by noodles and cheese October 06, 2011
To be the fastest bart around (from the hitch hikers guide)
Mike truely is the most slarty of us all
by the slart man February 05, 2009