Theory

“Yada, yada, yada” is an early 20th century equivalent of “blah, blah, blah.” It is American, and emerged during or just after the World War II. The alliterative saying was preceded by various alternative forms – “yatata, yatata,” “yaddega, yaddega,” et cetera. An example is found from an advertisement in an August 1948 edition of the Long Beach Independent:

“Yatata . . . Yatata” . . . The talk is all about Chatterbox, Knox’s own little Tomboy Cap with the young, young come-on look!”