Pronounced /məʊˈveɪ kuːˈʃəː/, the phrase mauvais coucheur designates a difficult, uncooperative or unsociable person.

This phrase occurs, for example, in a story on how leading Quebecers supported Jacques de Bernonville (1897-1972), a French war criminal who fled to Canada after the Second World War—story by George Tombs, published in The Gazette (Montreal, Quebec, Canada) of Saturday 24^th September 1994:

Bernonville’s trail in Quebec from 1946 onward is outlined in a secret 1949 RCMP [i.e., Royal Canadian Mounted Police] report sent to the deputy minister of mines and resources, the department then responsible for immigration.
The report revealed that Bernonville and several other French fascist fugitives had been put up at Kerhulu’s, a well-known hostelry in Sillery, a Quebec City suburb. Money for each arrival was provided by two men, both from France: businessman Jean Bonnel, described in the report as “not very intelligent, prone to flattery, pompous, a bit naïve . . . an out and out Pétainiste;” and businessman Jacques Fichet, “well off, haughty, loves to dominate, mauvais coucheur (a person acting in bad faith) and envious, hates the English . . . very Pétainiste and pro-Vichy.”

The phrase mauvais coucheur is a borrowing from French: the French adjective mauvais means bad, the French noun coucheur designates a bedfellow, and the French phrase mauvais coucheur originally referred to a person whom a traveller had to share a bed with when stopping over at an inn.

This original reference was mentioned in Le Dictionnaire de l’Académie françoise (Paris: Chez la Vve de Jean Baptiste Coignard, 1694), in which the French phrase mauvais coucheur occurred as follows:

1-: s.v. coucheur:

Quand nous sommes en voyage nous couchons ensemble luy & moy, c’est mon coucheur. […] bon, commode coucheur. mauvais, meschant, incommode coucheur.
     translation:
When we travel we share a bed he & I, he is my bedfellow. […] good, easy-going bedfellow. bad, nasty, difficult bedfellow.

2-: s.v. couverture (i.e., blanket):

Il est mauvais coucheur, il tire toute la couverture à luy ¹, les draps & la couverture.
     translation:
He is a bad bedfellow, he draws all the blanket to himself ¹, the bedsheets and the blanket.

¹ The French phrase tirer (toute) la couverture à soi, literally to draw (all) the blanket to oneself, is used figuratively to mean to take the credit.

The earliest occurrence of the French phrase mauvais coucheur that I have found is from Tesoro de las tres lenguas francesa, italiana, y española. Thresor des trois langues, francoise, italiene, et espagnolle (Geneva: Philippe Albert & Alexandre Pernet, 1609), by Girolamo Vittori, who equated un mauvais coucheur with un homme de mauvaise compagnie, i.e., a man who is bad company:

Hómbre de mála yazíja, vn mauuais coucheur: vn homme de mauuais [sic] affaire, de mauuaise compagnie, vno maluagio compagno in letto, vno huomo di cattiua vita, & compagnia.

The earliest occurrences that I have found of the phrase mauvais coucheur in English texts are as follows, in chronological order:

1-: From The Saint James’s Chronicle, and General Evening Post (London, England) of Thursday 19^th November 1829:

The French Papers of Tuesday state that considerable disagreement exists in the French ministry, and that M. de la Bourdonnaye ² has vehemently opposed the appointment of Prince Polignac to the Premiership. M. de la Bourdonnaye, our neighbours say, is a mauvais coucheur, i.e. a bad bedfellow, which means that he cannot agree with any one; and it is generally considered that he must go out.

² This refers to the French politician François-Régis de La Bourdonnaye (1767-1839), Comte de La Bretèche.

2-: From a correspondence from France, published in The Examiner (London, England) of Saturday 25^th February 1843:

M. de Tocqueville ³ has not come off best from his démêlé with Lord Brougham ⁴. His Lordship, however, was not only harsh in his remarks, but moreover chose a bad time for them; for M. de Tocqueville, thinking the old Liberal opposition of M. Barrot and Co. to be common-place and ineffective, had just undertaken, in association with his friend De Beaumont, with Lamartine ⁵ and others, to set up a new and much more powerful opposition. M. de Lamartine declared that it was to be nothing less than French Whiggism. The boat of this new political party had been but just launched in all the glory of new paint, sails, and rigging, when Lord Brougham chooses to run athwart the handsome craft in his d—d old lugger. He nearly upset the little pinnace of Admiral Tocqueville, who was dreadfully incensed, and who swore at his Lordship in the response, which you have seen.
Most people in Paris condemn Lord Brougham, not for being in the wrong, for all are agreed that Tocqueville knew nothing of the actual stipulations of the Treaty of 1834 with America, however he might have heard of its existence, and therefore his marvellous ignorance was too true an accusation; but then Lord Brougham is a French academician, and for brother academicians, especially of the Academy of Political Science, to accuse each other of marvellous ignorance, especially in a piece of political science, is something worse than insult—it is treason. Accordingly Lord Brougham has obtained in Paris pretty much the same character which he enjoys at home—viz., that of being a mauvais coucheur.

³ Alexis de Tocqueville (1805-1859) was a French political scientist, historian and politician, best known for De la Démocratie en Amérique (1835-40).
⁴ Henry Brougham (1778-1868), 1^st Baron Brougham and Vaux, was a British statesman.
⁵ Alphonse de Lamartine (1790-1869) was a French poet and statesman.