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.

1. Blue Monday is the most depressing day of the year, calculated by Dr. Cliff Arnall, a researcher at the University of Cardiff's Center for Lifelong Learning.
Factors used to calculate the date included weather conditions, debt level, time since Christmas, time since failing our New Year's resolutions, low motivation and feeling the need to take action.

In 2005 the date was calculated as January 24th, in 2006 it was January 23rd, and in 2007 it was January 22nd.

2. A song by the hard rock band Orgy from their album Candy Ass.

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.