Green’s Dictionary of Slang

(Aus. prison) to get into trouble, to be punished.

1886

Eve. News (Sydney) 15 May 7/5: It was all up with our escape, and we knew we should get in for it.

(Aus.) to trick, to mislead.

1895

Truth (Sydney) 14 Apr. 6/2: Somebody has been ‘getting in’ on ‘Terlinger’ in the ‘Australasian’ with that yarn about The Barb being stolen when he was a colt.

(N.Z.) to conduct a relationship with, usu. amatory.

2003

McGill Reed Dict. of N.Z. Sl. 85: get in tow with Keep company, often of the kind that represents a loving couple. Mid C20.

(US) to establish a relationship with.

1931		W.R. Burnett Silver Eagle 88: Harworth hung up the receiver and sat smiling at Stein. ‘Well, well, well,’ said Stein. ‘I’m getting in right,’ said Harworth. ‘That girl’s away up there. She was Richard Magnussen’s wife; you know, the guy who made all that money in lumber’.
1943		W.R. Burnett Nobody Lives for Ever 8: ‘Look at my clothes,’ said Doc, bitterly. ‘How could I get in with a dame like that?’.

a general exhortation; in post-1980s UK, typically of a man’s friends who are watching his approaches to an unknown woman; often ext. as get in there, my son!

1927		M.C. McPhee ‘College Sl.’ in AS III:2 132: Freshmen are encouraged to study in such terms as: ‘join the cram session,’ ‘don’t upset the boat,’ ‘get in there and fight ’em’.
1944		Cab Calloway New Hepsters Dict. in Calloway (1976) 255: get in there (an exclamation): go to work, get busy, make it hot, give all you’ve got.
1944		‘Jiver’s Bible’ in D. Burley Orig. Hbk of Harlem Jive.
1971		(con. WWII) B. Aldiss Soldier Erect 135: I wouldn’t mind slipping her a length [...] Wherrr! Git in there, Nobby!
2001		K. Waterhouse Soho 70: ‘Can I buy you a drink, Miss Wise?’ Making a coarse guttural sound, the first flyman urged: ‘Get in there, son!’.
2005		P. Howard Curious Incident of the Dog in the Nightdress 27: You’re trying to get in there. You’ve always had a thing for her.