Green’s Dictionary of Slang

1. (US) to start a fight; to fight; lit. and fig.

1906		T.A. Dorgan in Zwilling TAD Lex. (1993) 105: The boys are going to the ring with the idea of getting it on with the other fellow a bit.
1949		‘Hal Ellson’ Duke 89: Right after the party we was supposed to jump you, get it on.
1959		A. Anderson ‘Schooldays in North Carolina’ in Lover Man 101: I got you on two counts, so come on, son, let’s git it ON!
1972		C. Fuller Jr ‘Love Song for Wing’ in King Black Short Story Anthol. (1972) 146: ‘Let’s git it on!’ Cornbread backed up, his fists in the air.
1983		N. Heard House of Slammers 3: Two more wanted to fight and clearly longed for some excuse to get it on.
1993		T. Jones Pugilist at Rest 216: Yer a bluidy tough bloke, I cannae wait to get it oan.
1999		J. Ridley Everybody Smokes in Hell 128: A cycle and a pickup get it on, the pickup’s always going to win.
2002		‘Touré’ Portable Promised Land (ms.) 159: We Words (My Favorite Things) [...] Lay it on me. Layin in the cut. Let’s get it on.

2. (orig. US black) to start, to take positive action.

1968		‘Sl. of Watts’ in Current Sl. III:2.
1972		‘Soulful Spider’ ‘Pimp in a Clothing Store’ in Milner & Milner (1972) 288: Hey looka here, man, is my stuff ready? I mean you ain’t jivin’ around, is you? I’m out here doin’ it. I can’t be running around with these lames now. I mean, you know, git it on.
1992		A. Duff One Night Out Stealing 53: I just whacked at a ball [...] I knew this was it, cuzzy; we are gonna to be getting it on.
1993		I. Welsh Trainspotting 65: Let’s go for it cats, let’s get it on.
2000		J.J. Connolly Layer Cake 65: If the mood takes me, I like to get it on.

3. to get an erection.

1971

J. Mandelkau Buttons 54: I couldn’t get it on no matter what she did to me.

4. to enjoy oneself.

1974

Eble Campus Sl. Mar. 3: get it on – to have a good time: Let’s get it on!

5. (also get it on with, g.i.o.) to seduce, to have sexual intercourse.

1971		J. Mandelkau Buttons 90: The whole house was full of naked people getting it on.
1988		P. Califia Macho Sluts 31: Masturbation is [...] every bit as valid as getting it on with a partner.
1993		Snoop Doggy Dogg ‘Gin and Juice’ 🎵 I got bitches in the living room gettin’ it on.
1999		Guardian Editor 5 Nov. 18: Did you get it on with any of the chicks?
2004		P. Howard PS, I Scored the Bridesmaids 145: Her sister wants to get it on with me.
2005		Jade LB Keisha the Sket (2021) 26: y didnt i gt it on wit him earlier?
2010		K. Richards Life 214: Hey, baby, how you doing? Come on, let’s get it on.
2015		I. Welsh Decent Ride 325: As if ah fuckin care that they’re gittin it oan — ah fuckin well set the cunts up.
2018		G. Gilmore Class Act [ebook] ‘Charlie and I got it on‘.