What's the "een" in Halloween?
1940s, "masturbator," British slang, from wank "to masturbate," of unknown origin. General sense of "contemptible person" is attested from 1972. Cf. sense evolution of jerk (n.).
[origin unknown; perhaps fr British dialect wank, ''a violent blow,'' and semantically analogous with beat one's meat, whack off, pound one's peenie, etc]