The antithesis of what a good boy should be - rude, obnoxious, violent and stupid. Formed by spelling 'boy' bacwards, it was coined in England in the 18th century as it was very popular amongst upperclasses to speak backwards at the time.

A massive dump that takes 10 to 15 times to flush.

A thugish young male.

Yobs:

Primarily British slang

Delinquent teenagers with their hoods up (as defined by the Tory party).

hooligan, ruffian

"Yobbo or yob is a slang term for an uncouth or thuggish working-class person. The word derives from a back slang reading of the word "boy" (boy or boyo reversed becomes yob or – slightly modified – yobbo)."

Definition borrowed from Wikipedia.

Mentioned in British Civilization: An Introduction by John Oakland (p.13).

A yob is a job that is tedious and/or pays a very low wage. Refers to the working conditions (and the way Mexicans would pronounce j-o-b in Spanish) of Mexican Americans.