It's one of the most bad words that can be found in Neapolitan language. The word literally in Italian means "semen", can indicate a clever person, in this case the person is called " son of sfaccimma "that is not offensive. The origin is from Italian " sfacciato "
Be careful as to use this word why it's true that there are many " son of sfaccimma" but equally true that there are also many " men of sfaccimma "(people of no value). You can even say " ma che sfaccimma " that means " damn!"

When you eat dirt for the first time and leave your family to build a shack in the woods