The origin of the word is unknown, as it was overheard on a Scottish train by a group of neds, as they parleyed insults with each.
After much debate, it was decided that the word probably relates to a bin bag, with "scaff" being a slang term for rubbish/dirt, and a "bag" being a common receptical for objects.
Not to be confused with "Scaftag", an advertisement medium associated with scaffolding.
Ned 2- "Haw, you're a pure mad scaffbag by the way"
"I say, that scaffbag is stealing my car!"