Usually with a modifying word, the phrase piece of work colloquially denotes a person of a specified kind, especially an unpleasant one.

The literal meaning of piece of work is something produced or manufactured. It is first recorded in a “bill of supplicatioun” that the hatmakers presented on 18^th February 1473 to the Burgh of Edinburgh—as published in Extracts from the Records of the Burgh of Edinburgh. A.D. 1403—1528 (Edinburgh: Printed for the Scottish Burgh Records Society, 1869):

We the maisteris and craftsmen of the Hatmakeris thinkis it needfull and speidfull for the gude and treuth of the craft that all the saidis maisteris and wther that thinkis to be maisteris mak twa peis of wark sufficient belanging hattis-making.
     translation:
We the masters and craftsmen of the hatmakers think it needful and efficacious for the good and truth of the craft that all the said masters and others that think to be masters make two pieces of work that be obligatory for hat-making.

The phrase piece of work came to also denote an arduous task, a difficult undertaking. This is first recorded in Floures for Latine spekynge selected and gathered oute of Terence, and the same translated in to Englysshe, together with the exposition and settynge forthe as welle of suche latyne wordes, as were thought nedefull to be annoted, as also of dyuers grammatical rules, very profytable & necessarye for the expedite knowledge in the latine tongue (London: Thomas Berthelet, 1534), by the English schoolmaster and playwright Nicholas Udall (1504-1556):

Suarum rerum satagit ¹. He hath ynough to do of his owne, or, he hath a busye piece of werke of his owne to doo.

¹ The Latin phrase suarum rerum sat agit means has his hands full with his own affairs.

The phrase piece of work came to also denote a commotion, a fuss—as in the following from the account of the trial of several persons, charged with conspiracy and riot, published in The Sporting Magazine or Monthly Calendar, of the Transactions of the Turf, the Chase, and every other Diversion interesting to the Man of Pleasure, Enterprize & Spirit (London, England) of September 1810—the verb jaw means to address abusively:

Q. What else did you see? A. There was a donkey brought forward by Archer, and Bowman got upon the donkey, but we stopt him, and made him get off; he was then very abusive, and noisy; he kept jawing us, and making a piece of work all the time.

The English poet and playwright William Shakespeare (1564-1616):

– applied the phrase piece of work to man in The Tragicall Historie of Hamlet, Prince of Denmarke (London: Printed by James Roberts for Nicholas Ling, 1605):

Ham. What peece of worke is a man, how noble in reason, how infinit in faculties, in forme and moouing, how expresse and admirable in action, how like an Angell in apprehension, how like a God: the beautie of the world; the paragon of Annimales.

– characterised the painter as a filthy piece of work in The Life of Tymon of Athens (London: Printed by Isaac Jaggard and Edward Blount, 1623):

Tim. How lik’st thou this picture Apemantus?
Ape. The best, for the innocence.
Tim. Wrought he not well that painted it.
Ape. He wrought better that made the Painter, and
yet he’s but a filthy peece of worke.

One Captain A. Cameron used the phrase piece of work derogatorily of a person in a letter that he wrote to the Earl of Oxford in 1713—as published in Report on the manuscripts of His Grace the Duke of Portland, K.G., preserved at Welbeck Abbey. Volume X. Edited by R. F. Isaacson (London: Published by His Majesty’s Stationery Office, 1931):

Capt. A. Cameron to [the Earl of Oxford.]
[1713, July 24.] London.—I am overjoyed to understand that your Lordship is better this day. I understand there is one Campbell of Glenderuall come up here and keeps himself incog: with Sir John McLene who I doubt not has encouraged his coming up and designs to present him to your Lordship when it pleases God that your Lordship is in condition to see company. I believe he may have some message from Breadalbane; if so, I am sorry his lordship should employ one of this Campbell’s character which is not unknown to your Lordship when he was prisoner here and discovered everything he knew and much more. I believe your Lordship will have nothing to do with him he being a whidling ², dangerous, piece of work and not to be trusted, so that I hope when Sir John brings him there you will be pleased to tell that your Lordship will take your own way of dealing with Breadalbine, besides that my Lord Glenarcha is here who is certainly a better man than Glenderuall. I thought fit to acquaint your Lordship of this that you may give them what answer you think fit.

² The verb whidle (also whiddle, whidel, widdle) meant to divulge a secret, to turn informer.

The phrase a nasty piece (also a nasty bit) of work (also of goods) denotes an unpleasant, contemptible or cruel person. It is first recorded in The Good Genius that Turned Everything into Gold; or, the Queen Bee and the Magic Dress. A Christmas Fairy Tale (London: David Bogue, 1847), by the English journalist, author and social reformer Henry Mayhew (1812-1887) and his brother, the English journalist and author Augustus Mayhew (1826-1875):

Well! certainly some people seemed to take no pride in their wives’ looks!—He ought to have had a nasty slommicking ³ bit of goods, with her things all hanging about her anyhow, and then he’d have found out the difference.

³ This is one of the spellings of the verb slummock, meaning to behave in a lazy or slovenly way.