What's the difference between impolite and underbred?

Impolite

Definition:

(a.) Not polite; not of polished manners; wanting in good manners; discourteous; uncivil; rude.

Example Sentences:

(1) Lebedev said it would be "impolite" for him to think about any influence on British politics.
(2) 2) Subjects who received impolite messages showed positive attitude change toward computers despite the impolite messages.
(3) But we suppress so much just because it's impolite."
(4) Subjects became aggressive when impolite message were given repeatedly.
(5) But there is also the legendary case of the renowned South Korean director Shin Sang-ok who was actually kidnapped in 1978 from Hong Kong on the orders of Kim Jong-il who wanted him to make films promoting the good name of North Korea — the South Koreans evidently accepted (or thought it impolitic publicly to dispute) Kim’s claim that Shin had come willingly.
(6) To be impolite, it is theft," he said , branding search engines such as Google and Yahoo as "content kleptomaniacs" .
(7) And Gehry has a history of struggles with boards and impolitic comments.
(8) The frontrunner has spent much of the campaign apologising for impolite remarks about neighbours.
(9) But before the night ended, Minaj responded to criticism from the show’s host, Miley Cyrus, who had said in a New York Times interview last week that Minaj’s criticism was impolite and came from a place of jealousy.
(10) "But be punished in a way where people don't feel the managers are strange or weird or impolite people, or people without control."
(11) Taking a mobile phone picture of the emperor or his family is also considered impolite.
(12) I do, partly because it seems ungrateful and impolite not to, and partly because there's nothing else, really, to call oneself while retaining any connection to an original sense of justice.
(13) She declined to say how old she was, deeming it an “impolite question”, saying instead: “If you really need a number then go ahead and make it up based on my photographs”.
(14) Randall’s occasionally impolitic remarks made national headlines such as in 2010 when he referred to the national broadcaster as “Gay-BC”, and again in 2011 when he accused the mining industry of being “pussy -whipped” by Rudd’s successor, Julia Gillard, over the proposed mining tax.
(15) I believe at the end of the day I'll be seen as the 'impolite guy', the one who's aggressive in his words.
(16) But Judt's willingness to voice, as the New York Times recently put it, "impolite truths" brought attacks from fellow intellectuals.
(17) To act otherwise would have been “aggressive” and impolite.
(18) 5.05pm BST 1 min: The Dutch allow Australia to get some early touches at the back without any impolite pressure.
(19) Indeed, while the point of this study was to examine the medical profession's use of placebos, nobody seems impolite enough to point out that there are times when it's the patients' own fault if they end up smarting from a saline injection they didn't need.
(20) Giddings said that although he did not believe he had undermined or personally criticised Welby, he had apologised to the archbishop, who had since told him he had found nothing offensive, discourteous, impolite or disrespectful in his words.