Green’s Dictionary of Slang

come off v.1

1. (US) to stop, to refrain from a course of action; usu. as come off! excl.

[US] Century Dict. 73: Come off, to cease (fooling, flattering, chaffing, or humbugging); desist: chiefly in the imperative ... (Recent slang, U.S.).
[US]Bee (Earlington, NY) 12 Sept. 4: ‘Aw, come off. Go take a run [...] Youse gives me a pain’ ‘Come off yourself. See?’.
[Aus]Truth (Brisbane) 18 Nov. 8/1: Mr Waddlekin: They wouldn't take a bribe if it were bequeathed to them by an unknown testator. Mr. Snagglewit: Oh, come off, Waddlekin!
[US]G. Bronson-Howard God’s Man 376: Come off with that small-time humor. It even gets the hook in burlycue.
[NZ]N.Z. Truth 29 Dec. 4/6: Don’t be a blithering idiot. Come off that talk, now.
[US]C. Willingham End as a Man (1952) 36: Come off that crap. Keep your jaw shut.

2. (US) to hand over reluctantly.

[US]M. Braly Felony Tank (1962) 48: He’s got to come off that watch.

In phrases

come off the bird-lime

a general phr. of disbelief, ‘you must be joking’, ‘you don’t fool me’.

[UK]J. Manchon Le Slang.
come off the (tall) grass

(orig. US) stop telling lies, stop exaggerating.

[UK]Farmer & Henley Sl. and Its Analogues II 161/1: come off the grass, or the tall grass! phr. (American) — ‘None of your airs!’ ‘Don’t put it on so!’ ‘Don’t tell any more lies!’.

In exclamations

come off it! (also come out of it!)

stop it! don’t keep trying that line!

[UK]Marvel 19 June 15: Here, come off it, Carson!
[US]J. Lait Put on the Spot 165: ‘Where’s Goldie?’ he asked in a confidential tone. ‘Goldie? Goldie who?’ returned Monky, with a dead pan. ‘Come out of it,’ protested the officer.
[UK]E. Raymond Child of Norman’s End (1967) 439: Come awf it! You’ll make a joke in a minute.
[UK]C. Day Lewis Otterbury Incident 48: Me sing in the streets? Come off it, Ted!
[UK]Wodehouse Jeeves and the Feudal Spirit 58: Come off it. You know you’re in love with her yourself.
[US]M. Spillane Return of the Hood 12: ‘Come off it, baby,’ I told her softly.
[Aus]R. Macklin Queenslander 274: Come off it.
[UK]A. Payne ‘You Need Hands’ in Minder [TV script] 36: Come off it, Matthews, you’re no heroin dealer! Where did the stuff come from?
[US]T. Wolff ‘Missing Person’ in Back in the World 36: ‘Jerry, it isn’t true.’ ‘What isn’t true?’ ‘I never killed anyone.’ Jerry smiled. ‘Come off it’.
[UK]K. Sampson Powder 398: ‘There must be a mistake. I don’t think I ...’ ‘oh, come off it, will you!’.
[US]J. Lerner You Got Nothing Coming 295: ‘I don’t normally talk about people behind their backs’ [...] ‘Luther, come off it! Talking about people behind their backs is what you do best!’.

SE in slang uses

In phrases

come off one’s game (v.)

see under game n.

In exclamations

come off the roof!

used to an equal who is considered to be ‘getting above themselves’, ‘stop acting so superior’.

[US]N.Y. Times 26 Aug. 6/5: A still more recent example of slang is the ironical request of the street boy to a conceited and boastful opponent to ‘come off the roof.’ The request needs no explanation. It is vivid and picturesque. The world is full of men who might properly be requested to ‘come off the roof’.
[UK]W. Pett Ridge Minor Dialogues 86: ‘Come off the roof,’ says I.