Tumbling upside down, topsy-turvy.
‘Ass over teakettle’ is one of many variants of an expression meaning ‘head over heels; topsy-turvy; in confusion’. The usual British version is ‘ass over tip’ (or tit), which occurs in James Joyce’s Ulysses, among other works. This form also occurs in America. For instance, in The Grapes of Wrath Steinbeck has a character say, “You jus’ scrabblin’ ass over tit, fear somebody gonna pin some blame on you.”
J.E. Lighter, The Random House Historical Dictionary of American Slang (1994) notes such alternative ‘ass over X’ formulations—all with the meaning ‘head over heels’—as ‘ass over tit’ (from 1938), ‘ass over appetite’ (from 1942), and ‘butt over teacups’ (from 1954). Robert Chapman & Barbara Kipfer, Dictionary of American Slang, (1995), on the other hand, considers the original wording in the United States to have been ‘ass over tincups’ and reports the phrase as “a variant of the early-20th-century British ‘arse over tip.’”
The earliest known example of the phrase is in an 1899 book about Virginia folk expressions, which defines ‘ass over head’ as ‘head over heels; topsy-turvy.’ ‘Ass over head’ is a logical expression for a messed-up situation, as opposed to ‘head over heels,’ which is the natural way we appear when not falling down. A 1943 book about Indiana dialect in the 1890s lists ‘ass over applecart,’ and ‘ass over endways.’ The common ‘teakettle’ variation is first found in a 1946 book about fighter pilots in WWII, in a euphemized form: “He displayed a rump-over-tea-kettle aggressiveness in seeking dog-fights.”
While ‘teakettle’ may seem strange, imagine you are carrying a teakettle on a tray. The teakettle is up and your tail is below. If the reverse situation is happening, the tail is up and the teakettle is down.
This may go back to when afternoon tea was taken outdoors, perhaps in a pavilion or a gazebo. There would be steps going up into the structure where tea was served. If the server fell off the steps, his body would fall forward (dropping the tea kettle to the ground); the ass would naturally fall over the tea kettle.
‘Heels over tea-kettle’ appeared in Alfred Damon Runyon’s, “Fat Fallon,” in Lippincott’s Magazine (October 1907).
The earliest instance of ‘tail over teakettle’ is from Everybody’s Magazine (1927):
“Henry puts out a friendly paw. Gravy whirls, lashes out with her hind feet and lands on Henry’s ribs—biff—biff—and knocks him tail over teakettle.”
And the earliest instance of ‘ass over teakettle’ appears in Richard Johns, Pagany, volume 3 (1932):
“If I was him I would of fired you ass over teakettle out of the place on the spot for carelessness.”
The only slang meaning of ‘teakettle’ by itself appears in the Dictionary of American Slang, (1960):
“teakettle n. An old locomotive. 1952: Railroad use.”
That makes sense to me. I can imagine the old steam locomotives belching steam from the stack, just like a teakettle at full boil belching steam from the spout.