"One born outside of the city wall of Dublin. The large encircling wall was called the pale, hence the origin of the term. Also a term indicating one who is acting in an unreasonable fashion, (in Ireland reason is restricted to within Dublin, but thats a myth :p)

    Another term with slightly more derogatory connotations is Culchie, but if you ask them they would tell you that you had been talking to some Jackeen and to pay no heed."

    siren.beyong the pale,www.everything2.com, (July 2000).

There was some serious research that went on in order to understand the amusing anecdote siren alludes to. A best guess from some lay readers might be that the phrase describes something that is ‘out of the ordinary’ and that would be pretty close. The adjective pale meaning pallid or wan dates from the early 14th century, however it is pale as a noun that this phrase refers to from a couple of centuries earlier. Derived from Latin palus meaning stake, the Latin root lives on in English words such as impale. A pale is a wooden stake or a fence made from these wooden stakes. To enclose with pales means to fence in.

During the 15th and 16th centuries the dominions of the English in Ireland, Scotland, and France gave rise to the "boundary" sense of pale designating a particular geographical region with clear limits. Hence, beyond the pale referred to any area outside this controlled province. Lands beyond these ‘English Pales’ were considered uncivilized, and populated by barbarians. To journey outside of that boundary, beyond the pale, was to leave behind all the rules and institutions of English society and people looking to escape British domination were said to leap the pale when they passed the area's boundaries.

Over time, pale developed an additional metaphorical sense denoting the confines within which one is privileged or sheltered; as from censure. So, to be beyond the pale in this manner was to be outside the limits of protections. Today, the phrase is most frequently used to describe behavior regarded as appalling or coarse, as in:

    "He's out there operating without any decent restraint, totally beyond the pale of any acceptable human conduct. And he is still in the field commanding troops."
    - General Corman, Apocalypse Now, 1979.

"Beyond the pale," meaning to be outside the bounds of propriety or good taste, can be linked back to ancient England, armies and things like that. Writers enjoy the use of figurative speech to get at complex ideas. Oftentimes they are created to by-pass the language that developed in more constrained circles. Many today use the phrase 'beyond the pale' without knowing that the 'pale' was the area that encircled Dublin under English jurisdiction during the colonization of Ireland. Some etymologists say the seeds for the metaphor for the limit between what is legitimate and what is indecent can be found in one of William Shakespeare's earliest historical plays Henry VI. At this moment in the drama the hero of the tale, Talbot finds himself trapped; not literally trapped in this case since the French Dauphin’s army is just approaching, he has not yet had enough time to set up fortifications against a counter-siege:

Talbot:

Talbot is likely implying that he is in a closed space even though it is without walls. It feels as if he and his men are trapped like deer. In heraldry a pale is a broad perpendicular stripe on an armament as well and Shakespeare plays on both senses of the word. Talbot as a general of the English troops in France is so feared by the French that, when he is imprisoned, archers watch him even while he sleeps. After being released, he defeats the French several more times, until he is trapped at Bordeaux, where he and his son are slain. Fighting for the honor of king and country, Talbot symbolizes a dying breed of noble and gallant soldiers. When he falls, the last of tradition of valiant knights whose sole desire is to fight for the glory of their homeland passes figuratively beyond the pale of English chivalry.

The English pale in 14th century France was the territory of Calais, the last English possession in that country. The most recent example of pales with respect to certain districts and provinces was the Pale of Settlement. it was an obligatory requirement for Russian Jews to reside in pales from 1791 up until the Revolution in 1917. This institution is a translation of chertá osédlosti meaning "pale (boundary) of settlement".

Another famous one is the Pale in Ireland established after England’s invasion of the country in 1172. Referred to in the introductory citation, it was that part of the country over which England had express authority. It changed from time to time, but was an area of numerous counties centered on Dublin. The first mention of the Irish Pale was in a document dated around 1446. Though there was an effort later in the century to surround the Pale by a bank and ditch, it was never finished and “there never was a literal fence around it” says one source.

Modern figurative phrases analogous to the idea of being beyond the pale would be off-the-wall, outside the bounds of morality, good behavior or judgment; as in unacceptable; outside agreed standards of decency, in bad taste. Indecorous would be a good synonym as are unseemly, improper, indelicate, crude, vulgar, tasteless, rude, discourteous, impolite, gross,boorish, churlish, uncouth, barbaric, barbarous, unrefined, and unpolished. The earliest known example of the idiom use as a metaphor appeared in A Legend of Montrose by Sir Walter Scott published 1819:

    So much had been written and said on either side concerning the form of church government, that it had become a matter of infinitely more consequence in the eyes of the multitude than the doctrines of that gospel which both churches had embraced. The Prelatists and Presbyterians of the more violent kind became as illiberal as the Papists, and would scarcely allow the possibility of salvation beyond the pale of their respective churches.
A model illustration by Charles Dickens dated 1837 can be found in his novel The Pickwick Papers:
“I look upon you, sir, as a man who has placed himself beyond the pale of society, by his most audacious, disgraceful, and abominable public conduct.”

Quite a passage of time occurs between Shakespeare’s and Scott's use of the phrase. One expert from World Wide Words explains that the expression may have been used earlier than Sir Walter Scott, “but it surely doesn’t date back to the period of the Irish Pale, or anywhere near. It is often said that it does come directly from that political enclosure, but the three-century gap renders that very doubtful indeed. The idea behind it is definitely the same, though.”

Sources:

Alright, Demeaning Demeanor, A Little Latin Goes a Long Way, A Nice Question, Is OK Alright? and Beyond the Pale.:
http://www.word-detective.com/back-q.html

The American Heritage® Dictionary of Idioms by Christine Ammer © 1997 by The Christine Ammer 1992

In Defense of Jargon:
eserver.org/bs/31/ives.html

The Phrase Finder:
http://phrases.shu.ac.uk/meanings/64100.html

Take Our Word For It :
www.takeourword.com/Issue049.html

World Wide Words:
http://www.quinion.com/words/qa/qa-pal2.htm

xrefer:
www.xrefer.com