A loutish person, usually male. A hooligan. Derived from the back-slang for BOY > YOB.
Back-slang is a secret language thought to have originated in Victorian England in which the written word is spoken backwards. It was used mainly by market sellers and barrow boys to have a private conversation behind the back of their customers to collude or pass off low quality goods at inflated prices.
“That yob knicked my fags, I”ll have his hide the next time I see him!”.