A pathetic attempt by people with no language skills to say something using only the words they know. Used by morons who don't know any words other than f*** and s***. There are many synonyms which are much more creative, interesting and precise in meaning:
shitfuck (noun)= retard, idiot, jerk, imbecile, punk, moron, cro-magnon, etc...
Reporter interviewing random person on the street: "So, what do you think about the economy these days?"
"Fuck this shit, shitfuck!"
Reporter: "Can you tell me where someone smarter is?"