Bob's your uncle
...And Bob's your uncle is an expression of unknown origin, commonly used in Britain and Commonwealth nations. Typically, someone says it to conclude a set of simple instructions, similar to the French expression "et voilà!".
"Bob's your uncle" is an exclamation that is used when "everything is all right" and the simple means of obtaining the successful result is explained. For example: "left over right; right over left, and Bob's your uncle – a reef knot". It is sometimes elaborately phrased Robert is your mother's brother or similar for comic effect. With his customary whimsical humour, P.G. Wodehouse extended it to "Robert's your father's nearest male relative".
A common explanation is that the phrase dates to 1887, when British Prime Minister Robert Cecil, Lord Salisbury decided to appoint Arthur Balfour to the prestigious and sensitive job of Chief Secretary for Ireland. Lord Salisbury was Arthur Balfour's uncle.
Another explanation is that it is related to the British General, Lord Roberts, nicknamed "Bobs". The British Army in India coined the term "Bob's your uncle" to indicate you had the good fortune of being related to the commanding general.
There have been several other slang expressions which included the word "bob", some associated with thievery or gambling, and, from the eighteenth century on, it was also a common generic name for someone one did not know. The difficulty with any of these explanations is that – despite extensive searching – the earliest known published uses of the phrase are from 1932, two from 1937, and two from 1938. (See these and other quotes in American Dialect Society list archived posts by Stephen Goranson.)
Bob as a slang term meaning "safety" is cited in the 1736 dictionary A Collection of the Canting Words and Terms, both ancient and modern. Bob is also a slang term for shilling, a former monetary unit and coin of the United Kingdom, which was used in such phrases as the Scouts' Bob a Job Week.
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- From Aristotelian to Reaganomics: A Dictionary of Eponyms With Biographies in the Social Science, by R. C. S. Trahair, Greenwood Publishing Group, 1994, page 72. Retrieved online from Google Books, 30 Jul 2012.
- Knickers in a Twist: A Dictionary of British Slang, by Jonathan Bernstein, Canongate U.S., 2006, page 65. Retrieved online from Google Books, 4 August 2012.
- A Collection of the Canting Words and Terms, both ancient and modern, used by Beggars, Gypsies, Cheats, House-Breakers, Shop-Lifters, Foot-Pads, Highway-Men, &c. by N. Bailey, London, 1737, Vol. II, and transcrib'd into XML Most Diligently by Liam Quin, 1736. 
- Turner-Lord, Jann (1992). Bob's your uncle: a dictionary of slang for British mystery fans. Fithian Press. p. 62. 9781564740229.