A group of disreputable people of low social position; the dregs of society.
Any glance at any online bulletin board or newspaper letters column makes it pretty obvious that people love to call each other names. This is hardly a recent development; the number of slang synonyms for 'stupid' are legion: thick, dumb, daft, brain-dead, etc, etc. and the number of colloquial phrases where these are used as insults is even longer. I keep a database of phrases and it includes hundreds of 'you are stupid' expressions, starting with 'a bear of little brain' all the way to 'two sandwiches short of a picnic'. In researching the origins of 'riff-raff' it has become clear that there are just as many disparaging words to describe people at the bottom of the social heap and that a large number of these are linguistically associated with the term 'riff-raff'. I've opted for the most common current 'riff-raff' spelling here, but the credentials of the term as a long-standing spoken insult is hinted at by the no less than 18 alternative spellings listed in the OED - no small achievement for so short an expression:
ryf raf, rif raf, rif-raf, rifraf; rifraff, rifraffe, rife-rafe, ryffe raffe, rifferaffe, riffe-raffe, riffe raffe, riffe ruffe, riffraffe, riff-raffe, riff raff, riff-raff, riffraff.
Despite having a long and healthy life, the term 'riff-raff' had a complicated birth, probably somewhere in France. As early as 1326, the Annales Paulini (the chronicles of the reigns of Edward I and Edward II) record the French term 'rifler' with the meaning of 'robber; plunderer'. The Anglo-Norman word 'raf' was used in the French moral text The Debate between the Body and the Soul, circa 1330, with an undefined but generally depreciative meaning. The seems to derive from the French verb 'raffler', 'to ravage' or 'snatch away'. It may be that the two words 'rif' and 'raf' were simply semi-rhyming variants of each other.
By 1338, Robert Manning of Brunne had translated Langtoft's Chronicle of England and included the line:
Hei tok alle riffe & raf. [The took every single piece]
At that stage 'rif and raf' meant 'everything; every little bit', which no doubt reflects the 'rifling; stripping' meaning and indicates that plunderers left little of value behind them.
The 'riff-raff' version that has come down to us appears in Gregory's Chronicle, circa 1470:
Many a man was mortheryde and kylde in that conflycte, I wot not what name hyt for the multytude of ryffe raffe. [Many men were murdered and killed in that fight. I don't know what to describe it due to the large number of riff-raff'.]
It is clear that, by that date, the meaning of 'ryffe raffe' related to people and was derogatory. It seems likely that the name 'riff-raff' had transferred from the plunder to the plunderer.
The meaning continued to change , more toward the current 'scum; dregs of society' meaning. In 1545, Roger Ascham's Toxophilus, the Schole of Shooting included it with that meaning:
The common wealthe can be contente to take at a fonde father's hand the rifraffe of the worlde.
The offshoot term 'raffish' has stayed in the language, although this has shaken off its original 'disreputable; vulgar' meaning, i.e. 'a member of the raff-raff', to become an almost complimentary term for someone who is attractively mischievous or stylishly rakish.