The noun funny bone designates a place behind the bony point of the elbow at which a knock results in a sensation of tingling pain in the forearm and hand; the sensation results from compression of the ulnar nerve, which lies just beneath the skin at this place.
In early use, funny bone was perhaps partly punning on the homophones humerus (denoting the bone in the upper arm) and humorous. At least, that is what the following paragraph, from The Morning Post (London, England) of Monday 31st December 1827, seems to suggest—the noun os means bone (cf. bonfire):
March of Intellect.—“What does the Surgeon mean by the os humorous?” inquired a modern thirster after knowledge; “I doesn’t know, Jack,” replied his equally sagacious companion, “unless he means the funny bone.”
The earliest occurrence of funny bone that I have found is from A Trip to Bath; or, A Peep at the Assemblies, published in The Universal Songster; or, Museum of Mirth (Volume III – London: Printed for John Fairburn, Simpkin and Marshall; and Sherwood, Gilbert, and Piper, 1826):
Spoken.] Well, here we are, all safe arrived at Bath.—D—n Bath, I was mad to come to Bath.—Then you’re come to get your head shaved, I suppose.—You puppy, you’ve no head to shave.—No, I’m a Whig.—’Pon my soul, this pump-room is an uncommon fine place.—I say, there’s old Suet, the butcher, playing cards.—How are you, Suet?—What are stakes?—Best rump, are a shilling; chuck, tenpence halfpenny.—I say, Tom, there’s a fine girl.—I’ll have a dance.—Tom, Tom, I wish you would not be so droll.—Droll! what d’ye mean?—I wish you’d keep your funny-bone out of my ribs.—Come, strike up; let’s have the Bath waltz.
The second-earliest occurrence of funny bone that I have found is from Humours of Bartholomew Fair, published in The British Minstrel, and National Melodist (Volume I – London: Published by Sherwood, Gilbert, and Piper, 1827):
Spoken.]—‘Oh, law! oh, law! I never was in such a scroudge in all my life. Bless me! bless me! how the folks do squeedge, to be sure:—I say, you sir, do you see what you’re about?’—‘No, I don’t, marm.’—‘Why, you’re pussing the funny-bone of my helbow right through that ere gemman’s back.’—‘Oh, I beg your pardon, marm.’
The American-English equivalent of funny bone is crazy bone. It was defined as follows in Webster’s International Dictionary of the English Language (Springfield, Massachusetts: Published by G. & C. Merriam Company, 1907):
Crazy bone, the bony projection at the end of the elbow (olecranon), behind which passes the ulnar nerve;—so called on account of the curiously painful tingling felt, when, in a particular position, it receives a blow;—called also funny bone.
The earliest occurrence of crazy bone that I have found is from a poem originally published in the Boston Post (Boston, Massachusetts), and reprinted in several U.S. newspapers—for example in the Vermont Journal (Windsor, Vermont) of Saturday 20th September 1845:
Breathes there a man with soul so dead,
Who never to himself hath said,
When he hath heedless bumped his head,
Or who when shaving in morning cold,
Hath gashed his chin with razor old,
And could this powerful word withhold,
Or who on ice or slippery stone,
Hath fallen and jarred his “crazy bone,”
And not exclaimed with angry tone,
When one’s suspenders give away,
While dancing brisk with ladies gay,
Where is the man can help but say,
The second-earliest occurrence of crazy bone that I have found is from More Relics and Curiosities, by ‘Scriber’, published in the Boston Investigator (Boston, Massachusetts) of Wednesday 6th January 1847:
Mr. Editor:—Being aware that the public interest in curiosities of this kind has somewhat subsided, I with some reluctance, and only by the request of a friend, draw off and send you a few more, being the next in order on my descriptive catalogue, my friend thinking them to be more valuable and curious than the preceding ones.
They are as follows:—
One of the horns of the scape-goat that bore all the sins of the Israelites to a land not inhabited.
The crazy-bone of a fanatic who wanted to elbow his way through the world in his own way.
A piece of sack-cloth, such as people used to repent in, and such as Job sewed upon his skin.