Green’s Dictionary of Slang

1. drunk; thus so-so-ish, somewhat drunk.

1732		Harlot’s Progress 57: But I am no Religioso; / And, by the way, our Priest was so so.
1756		W. Toldervy Hist. of the Two Orphans III 211: He is but so, so: I know it is low with him at present [...] he drinks hard.
1788		G.A. Stevens Adventures of a Speculist II 86: We have pleasure to inform the married gentleman, particularly those who, in their buckish days, have been a little so-so-ish, [...] that Stiffend Stays are again coming into fashion.
1809		B.H. Malkin (trans.) Adventures of Gil Blas (1822) I 155: We drank hard, and returned to our employers in a pretty pickle, that is to say so-so in the upper story.
1849		Sam Sly 17 Mar. 4/3: Mrs. Sly begs to say that Mr. Sly never comes home so-so, and, therefore, needs no management in the way Katharine alludes to.
1858		‘A. Pendragon’ Queen of the South 148: ‘Well, Jack, how do you feel now?’ ‘Rather so-so [...] a little groggy about my head.’.
1889		Dead Bird (Sydney) 3 Aug. 1/1: ‘Would you oblige me with half-acrown, please?’ observed a gentleman to the owner of the house, as he ambled home slightly so-so.
1895		Mirror of Life 9 Nov. 3/4: Returnng home more or less ‘so-so’.

2. ill, uncomfortable.

1848

Bell’s Life in Sydney 25 Mar. 1/3: Smith looked queerish, and felt ‘tarnation’ so-so.

3. sexually excited.

1883

‘Three Chums’ in Boudoir I 2: The sight of this pretty Fanny [...] makes me feel quite so-so. In fact that girl has given me the Irish toothache.

4. menstruating.

1937–84

Partridge DSUE (1984) 1108/2: mid-C.19–20.