Green’s Dictionary of Slang

1. confused, at a loss.

1880		Punch 4 Sept. 106: ‘Tomkin’s First Session.’ Rather mixed after twenty-one hours’ continuous sitting [F&H].
1902		E. Townsend Chimmie Fadden and Mr Paul 14: When I gets a ting explained by bote Duchess and Mr. Paul, I am worse mixed dan a Coney Island cocktail.
1914		Bulletin (Sydney) 19 Nov. 43/2: I guess yew hev me kinder mixed.
1996		W.D. Myers Slam! 263: ‘I’m mixed [...] Bianca is messed around bad because Ice is her old man and she wants to stick with him’.

2. slightly drunk.

1872		Leeds Mercury 29 Aug. n.p.: ‘Nottingham Police Report.’ ‘Was defendant drunk?’ ‘No, Sir, he was not drunk, and he worn’t sober.’ ‘You say he wasn’t drunk?’ ‘No, Sir, he was mixed.’.
1900		Bulletin (Sydney) 28 Apr. 11/3: Was once on a pleasure-trip round the world, and one night, as our ship lay in Naples harbor, several of us went ashore and had a wild and woolly time. Later on I was very mixed [...] and didn’t remember much about it.
1900		Bulletin (Sydney) 10 Nov. 14/1: We only had a quart of rum to start with, but with the aid of spirits-of-wine, tobacco and strong tea, we made it up to about a gallon of very good grog, so that when the buggy arrived things were a bit mixed.
1912		Bulletin (Sydney) 17 Oct. 47/2: No, I’ve had five already, and might catch cold if I had any more [...]. Besides, I might get mixed, and then my reputation would be gone.
1933		‘William Juniper’ True Drunkard’s Delight 226: He is [...] mixed.

3. (S.Afr. gay) of a male prostitute who operates as either active or passive partner.

2003

K. Cage Gayle 82/2: mixed adj. 1. male prostitute who operates as both active or passive in a sexual encounter, depending on the wishes of his customer [Johannesburg, 1930s].