U (Adjective)
Informal
Chiefly British
Language or social behaviour characteristic of or appropriate to the upper social classes. Ie., U-manners, U-ness.
An abbreviation of Upper Class, coined in 1954 by Alan S. C. Ross, professor of linguistics. The term was popularized by its use in Nancy Mitford's Noblesse Oblige (1956).
Reference:
OED2ROM
http://home.echo-on.net/~buzzcorr/U(Adjective) - LINGO.htm

NANCY MITFORD (1905-1973)
"Unabashedly snobbish and devastatingly witty, Miss Mitford achieved enormous success and popularity as one of Britain's most piercing observers of social manners."

"...
Indeed, one of Miss Mitford's pet concerns entered the history of obscure literary debates when, in 1955, she published perhaps her most famous essay on upper-class and non-upper- class forms of speech.

The essay sparked such a controversy in Britain, with responses from many major literary figures, that Miss Mitford was compelled a year later to bring out a thin book, "Noblesse Oblige,"
http://www.commonreader.com/cgi-bin/rbox/ido.cgi?0096
with her disquisition on the subject as its centerpiece.

Her argument, a set-piece even today among literary parlor games, was that the more elegant euphemism used for any word is usually the non-upperclass thing to say--or, in Miss Mitford's words, simply non-U.

Thus: It is very non-U to say "dentures"; "false teeth" will do. Ill is non-U; sick is U. The non-U person resides at his home. The U person lives in his house. And so forth.

Perhaps Miss Mitford and only a few others would have had the credentials to engage in this kind of argument. She was the oldest of six daughters of Bertram Ogilvy Freeman-Mitford, the second Baron Redesdale, who lived with Lady Redesdale at Swinbrook, the family estate in Oxfordshire.

The girls called their father "Old Subhuman." "My father and mother, illiterate themselves, were against education, and we girls had none though we were taught to ride and to speak French," Miss Mitford wrote in "Twentieth Century Authors." "I grew up as ignorant as an owl, came out in London and went to a great many balls." "

The Mitfords were no strangers to controversy. One sister, Unity, shot herself when war was declared because of her admiration for Hitler. Another, Diana was married to Sir Oswald Mosely, a well-known fascist, and was considered a threat to national security during WWII. Jessica lived in the USA and wrote of her childhood in "Daughters and Rebels."

For a full obituary of Nancy Mitford see:
http://www.nytimes.com/learning/general/onthisday/bday/1128.html

For a discussion of the English Class System see:
http://homepages.go.com/homepages/h/u/g/hugodavenport/write2.htm
Google on "Mitford" or "U and non U" to find out more.

Let me know if the URL's make the page go w-i-d-e and I'll take out the hot links.