Green’s Dictionary of Slang

1. deceitful or underhand practices.

1882		R.J. Burdette William Penn 247: Calling them together, probably desiring to let them know there was no funny business about him.
1887		H. Frederic Seth’s Brother’s Wife 198: Especially if Abe Beekman, up in Jay County, tries any of his funny work.
1901		Bulletin (Sydney) 7 Dec. 20/3: The man showed his teeth and snarled in reply. / ‘Here, come!’ I said, ‘no funny business. I want something to eat and drink.’.
1910		‘O. Henry’ ‘Compliments of the Season’ in Strictly Business (1915) 199: ‘Cheese the funny business,’ said Riley.
1914		Truth (Melbourne) 24 Jan. 11/3: Hold that man constable [...] don’t let him get away. There has been some funny work here.
1921		P. & T. Casey Gay-cat 76: If he tries any funny work, we’ll —.
1925		A. Christie Secret of Chimneys (1956) 198: The genuine article? I can’t stand for any funny business?
1929		‘Max Brand’ ‘The Ghost’ in Goodstone Pulps (1970) 61/2: I ain’t going to try no funny stuff.
1931		C.B. Yorke ‘Snowbound’ in Gangster Stories Oct. n.p.: ‘Give them the works if there‘s any funny business. Scram’.
1933		‘Goat’ Laven Rough Stuff 203: He would have pulled some funny stuff himself, for he didn’t know what fear was.
1938		F.D. Sharpe Sharpe of the Flying Squad 57: If you behave yourself, Joe, there won’t be any funny business.
1947		N. Marsh Final Curtain (1958) 219: You think that when we’re married I’ll begin to work in some funny business.
1949		(con. 1943–5) A. Murphy To Hell and Back (1950) 120: Drive her car into town; and don’t try any funny stuff.
1949		H. Miller Sexus (1969) 66: Listen, don’t start any funny work.
1953		L. Uris Battle Cry (1964) 152: Knock off the funny business.
1956		N. Algren Walk on the Wild Side 57: Here was one party who didn’t take funny stuff off anybody any more.
1960		B. Kops Dream of Peter Mann Act III: Jason, no funny stuff, bury me near the gasworks.
1963		H.E. Bates Oh! To be in England (1985) 380: No funny business. Back over there. Go on, back.
1970		D. Ponicsan Last Detail 26: Don’t try any funny stuff.
1971		Wodehouse Much Obliged, Jeeves 169: She, of course, assured that there would be no funny business, [...] withdrew her objections.
1986		L. Heinemann Paco’s Story (1987) 161: I carry a small hunting knife [...] just so everybody knows I ain’t gonna tolerate no funny business.
2007		UGK ‘Cocaine’ 🎵 I never came, with the funny business.

2. euph. for sexual activity.

1964		‘Charles Barrett’ Address: Kings Cross 49: I think I’ve heard them politely described as inspectors, whose job it is to see the kids have good clean fun with no funny business allowed.
2002		D.H. Sterry Chicken (2003) 72: I’ll crash here, but I’m warning you, no funny business.
2004		Kemp & Kokker Lonely Planet Romania and Moldova 327: The single rooms [...] can be shared by two people as long as they are of the opposite sex (no funny stuff going on here!).