Green’s Dictionary of Slang

aimless chatter.

1952–5		Lou Willie Turner ‘Honey Hush’ 🎵 Come in this house, stop all that yackety yack.
1957		Mad mag. Nov.–Dec. 15: I couldn’t get a word in edgewise. Yakkity-yakkity-yak!
1962		(con. WWII) J.O. Killens And Then We Heard The Thunder (1964) 49: Tell the lady what you want and stop taking up all of her time with the yackety-yack.
1970		D. Ponicsan Last Detail 173: ‘Everybody on the base is talking about you birds.’ ‘A legend in my own time, yakety, yakety, yak, yak, yak.’.
1979		E. Torres After Hours 185: Yakkity-yak for a longer spell.
1986		D. Barker Life in Jazz 161: ‘I had been getting the yackety yack from different people, saying, "He can't do that to you. Why don't you sue him?’.
1987		Boogie Down Productions ‘Elementary’ 🎵 I will [...] launch an attack / On you fake educators with your yakety-yak.
1992		R.C. Cruz Straight Outta Compton 17: Hitting us with all kinds of yacky-yack/mucty-muck.