The term Sloane Ranger (plurals: Sloanes, Sloanies) refers to the young, upper class and upper-middle-class men and women living in South-West London.

The exemplar Female Sloane Ranger (FSR) was Lady Diana Spencer before marrying Charles, Prince of Wales...

Typical of SRs were patriotism and traditionalism, an inflexible belief in the values of upper class and upper middle-class culture, self-confidence in themselves and their given places in the world, a fondness for life in the countryside, country sports in particular, philistinism and anti-intellectualism.

Applied to a younger, school-age generation, the term can also be seen as a generic term for confident, somewhat brash, private-school children.

http://en.wikipedia.org/wiki/Sloane_Ranger

chinless wonder"
a person of the wealthy upper classes, who lacks depth of character and/or intelligence
English Slang Dictionary v1.2
http://dictionary.babylon.com/Chinless_wonder

an English man from a high social class, who thinks he is intelligent and important, but who other people think is weak and stupid
"He's just another chinless wonder doing a job that his Daddy got for him."
Cambridge Idioms Dictionary, 2nd ed. Copyright © Cambridge University Press 2006. Reproduced with permission.
http://idioms.thefreedictionary.com/a chinless wonder

Brit informal
a person, usually upper-class, lacking strength of character
Collins Essential English Dictionary 2nd Edition 2006 © HarperCollins Publishers 2004, 2006
http://www.thefreedictionary.com/chinless wonder

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Note added at 2 hrs (2009-04-06 15:47:25 GMT)
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Um equivalente aproximado no Brasil seriam os "mauricinhos" e "patricinhas"

Patricinha
Origem: Wikipédia, a enciclopédia livre.

Patricinha (diminutivo do prenome Patrícia), também denominada Paty, é uma gíria brasileira que designa uma mulher, normalmente uma adolescente de alta renda, que tem uma preocupação excessiva em se vestir de acordo com a moda e que anda em grupos, com outras moças que compartilhem os mesmos valores.

No Brasil,o equivalente a patricinha na idade adulta costuma ser associado a socialite ou, no sentido pejorativo, perua, que é uma mulher casada que não trabalha e vive uma vida luxuosa, sustentada pelo seu marido.

O equivalente aproximado em Portugal, tanto para patricinha como para mauricinho, é “queque”.

Ver também:

http://pt.wikipedia.org/wiki/Mauricinho