“Yada, Yada, Yada” (“Yadda, Yadda, Yadda”; “Yatata, Yatata, Yatata”)

“Yada, yada, yada” was popularized by an April 24, 1997 episode of the New York City-based television sitcom Seinfeld. The 1947 Oscar Hammerstein II-Richard Rodgers musical Allegro contained a song called “Yatata, Yatata, Yatata,” about the nonsensical talk at cocktail parties. The origin of the nonsense term is unknown—perhaps it has its origins in “yatter.”
 
The repeating of terms such as “blah blah blah” or “yeah yeah yeah” dates much earlier than 1947. “Yap, yap, yap” is a similar form with a meaning of “talk, talk, talk.”
 
   
Wikipedia: The Yada Yada
“The Yada Yada” is the 153rd episode of the American NBC sitcom Seinfeld. The 19th episode of the 8th season, it aired on April 24, 1997.
   
“Yatata, Yatata, Yatata” lyrics
Track Title:  Cocktail Party
Prime Artist:  Unknown
Lyrics by:  Oscar Hammerstein II   (O. Greeley Clendenning H. II)
Music by:  Richard Rodgers
From the Show:  Allegro 1947 (S)
 
Lyrics:
Yatata, yatata, yatata, yatata,
Yatata, yatata, yatata, yatata,
 
Busy!
Busy!
I’m busy as a bee!
I start the day at half-past one.
When I am finished phoning
It’s time to dress for tea.
Nothing I have to do gets done!
 
(The deep-thinking gentlemen and ladies
Who keep a metropolis alive
Drink cocktails
And knock tails
Ev’ry afternoon at five.) (...)
 
(Oxford English Dictionary)
yada yada, int. and n.
colloq. (chiefly U.S.).
Forms: 19- yada yada, 19- yaddah yaddah, 19- yadda yadda, 19- yaddeyahdah, 19- yatta yatta. Also often reduplicated further. 
[Imitative of the sound of human speech, prob. influenced by (or perh. an alteration of) YATTER n. Cf. also the following:
1949 Sat. Evening Post 27 Aug. 98/4 ‘Back-seat flying,’ Mike would grumble. ‘Always the yaddega-yaddega from the back seat’.
1950 Time 30 Oct. 100/3 Though Right Cross’s ring scenes are pretty well staged, it is a boxing picture with too much yatata and not enough sock.
1956 Holland (Mich.) Evening Sentinel 4 Feb. 6/6 (caption) You heard about her husband, didn’t you? He won a trip to Bermuda… Well, he didn’t tell her, and yattata-yattata.] 
 
A. int.  Indicating (usually dismissively) that further details are predictable or evident from what has preceded: ‘and so on’, ‘blah blah blah’.
a1967 L. BRUCE Essential Lenny Bruce 182 They’re no good, the lot of them ‘Yaddeyahdah’ They’re animals!
1981 Washington Post (Nexis) 5 Jan. B1 I’m talking country codes, asbestos firewalls, yada yada yada. 
B. n.  Trivial, meaningless, or uninteresting talk or writing; chatter. Cf. BLAH n.
1991 Vanity Fair Feb. 144/2 This yatta-yatta is, of course, an evasion, and one that has..sparked endless speculation in Los Angeles about their relationship.
 
22 August 1919, Bridgeport (CT) Standard Telegram, “YAP! YAP! YAP!”, pg. 12, col. 2:
The great and only game of yap, yap, yap, came to a fitting climax when the Foreign Relations Committee of the Senate asked the President of the United States how old he was, where he was born and why, and if he could read and write. Well no, they didn’t ask exactly these questions, but they only skipped a few such.
 
28 January 1946, Dallas (TX) Morning News, section II, pg. 5:
...the presentation of the rose, buffo spirit in the musical “yatata” of the intrigants,...
 
13 July 1946, Dallas (TX) Morning News, section II, pg. 4:
For we are telling no secret when we say that the candidate at the microphone stumbles through words that somebody else wrote. Fifteen minute periods of yatata are interminably dull without the exercise of the subtlest radio art.
 
17 July 1946, Dallas (TX) Morning News, section I, pg. 8:
The new acoustical ceiling has almost been installed in the lobby, guaranteed to deaden the intermission “yatata.”
     
11 October 1947, New York (NY) Times, “Allegro Broadway review by Brooks Atkinson, pg. 10:
For Mr. Rodgers and Mr. Hammerstein are able composers in any vein, and they have some notable numbers for the modern portion of their play. “Money Isn’t Everything” is a skillful satire of materialism,; “Yatata, Yatata, Yatata” is a savage cartoon of cocktail parties,...
   
2 November 1947, New York (NY) Times, “‘Allegro” a Fragment of The American legend” by Brooks Atkinson, pg. X1:
Mr. Rodger and Mr. Hammerstein have written two clever songs for the second act—“Yatata, Yatata, Yatata,” which is a savage cartoon of the barbaric social function known as the cocktail party, and “The Gentleman Is a Dope,” which is superior blues music.
 
26 December 1947, Dallas (TX) Morning News, section I, pg. 4:
But who stops to think what the cook stands, day in and day out? Breakfast, lunch, dinner, stove, icebox, sink, garbage pail, yatata, yatata, yatata.
       
Jim Dandy: fat man in a famine
a play by William Saroyan
New York, NY: Samuel French
1947
Pg.?:
Yatata yatata yatata.
 
18 August 1948, Long Beach (CA) Independent. pg. 18, col. 1 ad:
Yatata ... yatata ... the talk is all about Chatterbox, Knox’s own little Tomboy Cap with the young, young come-on look!
 
19 September 1948, New York (NY) Times, pg. X5:
A TRIO OF YATATA, YATATA BOYS
(Three announcers—ed.)
   
25 February 1949, Nashua (NH) Telegraph, “Just Pitching” by John Wheeler, pg. 6, col. 2:
COCKTAIL PARTIES
(...)
The dialogue sounded like “yatata, yata, yatata.” (...) It just went on “yatata, yata, yatata.” Try it yourself sometime unless this warning cures you of the habit of cocktail parties.
 
21 January 1961, Capital Times (Madison, WI), “A Boy, His Bomb—And The Comic Books” by John Crosby (NY), pg. 18, col. 5:
The boy looked up, clearly irritated by all this yatata yatata. 
   
18 April 1961, Reno (NV) Evening Gazette, pg 16 (cartoons):
WHY’D YOU BRING ME THIS TIN CUP?
TO RATTLE ACROSS THE BARS AND YELL, YATTA, YATTA, YATTA, WARDEN!
(“Gordo” cartoon by Gus Arriola—ed.) 
 
Google Books
Language on Vacation
by Dmitri A. Borgmann
New York, NY: Charles Scribner’s Sons
1965
Pg. 175:
YATATA YATATA (monotonous talk, idle chatter).
 
Google Books
Two Small Bodies
a play by Neal Bell
New York, NY: Dramatists Play Service, Inc.
1980
Pg. 12:
EILEEN> (Imitating, tough.) “Don’t fuck with me or I’ll kill ya,” “Kick ass,” “Yadda yadda.”
 
Google Books
Sophie’s Choice
by William Styron
New York, NY: Bantam Books
1982
Pg. 50:
“Yatata Yatata all day long. I can’t stand that telephone.”