The noun armchair is used as an attributive modifier meaning:
– based or taking place in the home as opposed to the world or environment outside;
hence, chiefly depreciatively:
– lacking or not involving practical or direct experience of a particular subject or activity.
—Cf. also ‘parlour’ (attributive modifier): ‘parlour patriot’ and ‘parlour socialist’ | ‘parlour socialism’.

 

PHRASES THAT HAVE BEEN NON-DEPRECIATIVE AND DEPRECIATIVE:
ARMCHAIR TRAVELLER – ARMCHAIR SPORTSMAN

 

In the texts containing the earliest occurrences of armchair traveller that I have found, the phrase has no negative connotations; it simply denotes a person who discovers a place by reading a book about it.

These texts are:

1-: The review of Caledonian Sketches, or a Tour through Scotland in 1807 (London: Matthews and Leigh, 1809), by the English travel writer John Carr (1772-1832)—review published in The Monthly Review; or Literary Journal (London) of September 1809:

A great portion of this volume is occupied by a description of Edinburgh; which, while it instructs the arm-chair traveller, must be highly satisfactory to the Scottish nation.

2-: An advertisement published in several British newspapers in 1835—for example in The Morning Post (London, England) of Tuesday 21^st July:

The Danube.—The picturesque shores of this mighty river have not often been visited by English travellers. The Rhine has been described till one wearies of the name; but the grander Danube is comparatively unknown among us. Mr. Quin has just returned from a steam-voyage down the latter river, and summer tourists may learn by the narrative about to be published of his excursion what pleasures lie within their reach in a six weeks’ visit to the countries through which the Danube flows. In such a tour, and with so circumstantial a guide as will be furnished by Mr. Quin’s volumes, they may see many interesting parts of Hungary, Wallachia, Servia, and Turkey; and to the mere “arm-chair traveller” the perusal will open fresh and romantic scenes, and enlarge the sphere of his information.

3-: An advertisement for A Tour through the Valley of the Meuse (London: Chapman and Hall, 1845), by the Anglo-Irish soldier, journalist and author Dudley Costello (1803-1865), published in several British newspapers in 1845—for example in The Morning Post (London, England) of Friday 29^th August:

This tastefully illustrated volume will find its way not only into the hands of tourists who may propose to travel over the same ground as the author (in which case it will be found an excellent hand-book or guide), but into the study and library, where arm-chair travellers, for lack of means, or health, or time, are forced to visit foreign lands mentally.

But, in the following from The Field, The Farm, The Garden: The Country Gentleman’s Newspaper (London, England) of Saturday 28^th November 1874, the phrase armchair traveller denotes a person who, although having no practical experience of travelling, offers criticism on the subject:

English Travellers.

We are proud of our travellers. There is perhaps no other nation in the world which can show so long and unbroken a succession of self-sacrificing men, who, with the spirit of true adventure, have sought to penetrate unknown regions. Geography, as we know, is full of problems. The theories in which they are involved have for ages defied solution. Generally speaking, the active pioneers who set themselves to the hard task of endeavouring to unravel these complications, have not been the original speculators of the causes or proofs which they afterwards succeed in verifying. It is not right, in one respect, to sneer at armchair travellers, as geographers of maps and profound references are occasionally termed. Their suggestions may be of value, though their actual experience is not worth taking into account. They are, however, it must be said, now and again inclined to forget their functions; instead of being gratefully, they grow captiously critical.

In the following from Jackson’s Oxford Journal (Oxford, Oxfordshire, England) of Saturday 17^th January 1846, the phrase armchair sportsman has no negative connotations; it simply denotes a person who can no longer hunt, but who relives hunting by reading about it:

A finer season for that spirit-stirring amusement of fox-hunting has not been known for many years, and among the numerous splendid runs we will record one for enlivening those veteran arm-chair sportsmen, whose hearts still beat to the sound of “Tally-ho,” though their limbs are no longer adapted to the vibrations of the saddle.

But in the following from the Aberdeen Journal (Aberdeen, Aberdeenshire, Scotland) of Wednesday 15^th August 1883, armchair sportsman denotes a hunter who waits while the others drive the deer towards him—the forest is near Morvich, in Scotland:

Mr Winans, the American millionaire, […] rents over 200,000 acres of forest in this vicinity […]. What on earth Mr Winans can want with such extensive shootings as he possesses is a mystery. Nobody but his sons, it is said, ever shoots with him; and he bears the reputation of being one of those arm-chair sportsmen who gets the deer driven up to their guns.

And, in the review of Riding, Driving, and Kindred Sports (London: T. Fisher Unwin, 1899), by T. F. Dale, published in The Manchester Guardian (Manchester, Lancashire, England) of Saturday 10^th February 1900, armchair sportsman denotes a person who has no practical experience of sports—as opposed to the author of the book, who is a sportsman:

This is not a pretentious book, either in style or appearance, but it is crammed with most valuable suggestions and facts which are certainly not the production of an arm-chair sportsman.

 

PHRASES THAT HAVE ALWAYS BEEN DEPRECIATIVE:
ARMCHAIR CRITIC – ARMCHAIR GENERAL

 

The phrase armchair critic denotes a person who offers comment or criticism on a subject of which he or she has little or no practical knowledge or experience.
—Cf. also the phrase backseat driver, denoting a passenger in the rear seat of a car who gives the driver unwanted advice, hence, figuratively, a person who is eager to advise without responsibility.

The earliest occurrence of the phrase armchair critic that I have found is from the review of The War and the Newspapers (London: J. H. and J. Parker, 1856), by the Rev. C. E. Kennaway—review published in The Church Warder, and Domestic Magazine (London, England) of April 1856:

This is a lecture, which was delivered by the Vicar of Campden to the members of the Literary Institution, at Ottery St. Mary; and its object is, to counteract the evil effects which newspaper critics have done, and are still doing, to the noblest, the most powerful, and the bravest army that England ever sent out to combat her enemies. […] We strongly recommend this lecture; it will disabuse the minds of those who have placed too great reliance in feather-bed and arm-chair critics, and would-be generals.

The phrase armchair general denotes:
– a person without military experience who regards himself or herself as an expert military strategist;
– a military commander who is not actively involved in warfare, or who directs troops from a position of comfort or safety.

The earliest occurrence that I have found is from the Savannah Morning News (Savannah, Georgia, USA) of Friday 24^th July 1885:

Jacksonville, Fla., July 23.—[…] Universal regret was excited here by the announcement of Gen. Grant’s ¹ death. […] The daily Times-Union will say editorially to-morrow:
The Southern soldiers and commanders (and the world never saw better) tested Gen. Grant’s strong points, and it is peculiarly gratifying at this solemn moment to recollect the fact that not from them came the voice of detraction. Lee ² and Grant, and the officers and men on either side, respected one another. It was the armchair Generals who kept carefully in the rear of war that defamed and belittled both.

¹ The U.S. general Ulysses Simpson Grant (Hiram Ulysses Grant – 1822-1885) was the supreme commander of the Union armies during the American Civil War (1861-65); he served as the 18^th President of the USA from 1869 to 1877.
² The U.S. general Robert Edward Lee (1807-1870) was the commander of the Confederate army of Northern Virginia for most of the American Civil War.