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.

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.