Green’s Dictionary of Slang

1. a mild excl. of annoyance, euph. for a variety of ‘stronger’ synons. , e.g. fuck it! excl.

1820		Jack Randall’s Diary 8: [He] swore that blow his Sister’s wig, Tom Trot was free from reprehension.
1840		R.B. Peake Devil In London I ii: Hem! now I’ve got a cold in my nose – blow it! – and no pocket-handkerchief.
1848		Bell’s Life in Sydney 4 Nov. 2/5: ‘Oh, cri! my! oh! oh! blow it! no!’ cried James.
1854		‘Cuthbert Bede’ Adventures of Mr Verdant Green (1982) II 158: Oh, blow it, Gig-lamps [...] you’ll never go and do the mean, and show the white feather, will you?
1882		Nat. Police Gaz. (NY) 22 Apr. 2/3: Oh. blow it, Mayo, if you will play through the nose you can’t complain if you ‘pay through the nose’.
1892		H. Nisbet Bushranger’s Sweetheart 148: Blow it! [...] let’s have a shy at the business for ourselves.
1917		‘Henry Handel Richardson’ Aus. Felix (1971) 32: Oh, blow it, Dick, you’re too fastidious.
1947		(con. 1944) J.H. Burns Gallery (1948) 93: Ah, blow it ... I figure we’re going to Oran or Algiers for more of this base section life.

2. see blow it out your ass! excl.