Green’s Dictionary of Slang

go away! stop bothering me!

1919		S. Lewis Free Air 133: ‘Still, by golly, didn’t I pick up Dutch—German—like a mice? Back off, son! You did not! ’.
1975		E. Torres Carlito’s Way 96: Back off, motherfucker.
1981		J. Ellroy Brown’s Requiem 142: ‘Back off there, Brother Bob,’ I said. ‘I’m on your side and just making friendly overtures.’.
1992		in R. Graef Living Dangerously 153: Raga told him to back off and that.
2000		C. Cook Robbers (2001) 238: Listen, goddammit, why don’t you just back off a notch.