Having arisen from the adjective: 'ruthless': of 14th century Germanic origin to describe the lawless backwoodsmen infamous for lurking the fringes of Germanic forest land and hitting up the hallucinogenic ye olde fungi of the Black Forest, 'ruth' can be considered the shortened version of this same word with a similar meaning. It can be used particularly effectively as a pronoun in place of one's official birth name if they are displaying characteristics including but not limited to: taking a fuck load of pills, drinking a fuck load of spirits or doing a fuck load of fucking.
Gretel: Sheisse Viktor could you be any more ruth?
Viktor: honestly, nein
Jonny: fucking christ aye look at that ruth slut dance