Green’s Dictionary of Slang

soft thing n.

1. an easily duped simpleton.

[UK]Isle of Wight Obs. (Ryde) 7 Apr. 3/4: We admire timid and gentle things [...] and public men too like agreeable soft things, and look with applauding favour on the undescerning [sic] scribe.
[UK]Sporting Times 12 Apr. 2/3: Charlie Thompson won swimming match [...]. Charlie swam half-way under water, and other man never worried, as he thought Charlie had not started. Soft thing.
[US]Ade More Fables in Sl. (1960) 104: He was the Softest Thing the Lady Robber had Stood Up that Season.
[Aus]D. Stivens Tramp and Other Stories 26: This’s the guard who’s a soft thing, eh? ‘He’s a decent cove.’ I’ll make your tongue hang out!

2. something which requires no effort, an easy job, an easy win etc.

[US]Brooklyn Dly Eagle (NY) 24 Aug. 2/5: The Atlantics went to New Brunswick short handed, thinking they had a soft thing [...] and were defeated.
[US]L.H. Bagg Four Years at Yale 48: Soft thing, an easy place, a pleasant position, a sure chance.
[US]G.P. Burnham Memoirs of the US Secret Service 54: They had a soft thing of it.
[US]Butte Miner (MT) 27 July 3/3: Phillipsburgers supposing they had a soft thing came to Butte in full force [...] Sporting Butteites also imagined they had a soft thing.
[Aus]Bulletin (Sydney) 14 Mar. 14/2: According to all accounts, the slogger is carrying on a game which can’t last, and in twelve months time, bids fair to be a ‘soft thing’ for a really good man.
[Aus]H. Lawson ‘The Squatter, Three Cornstalks, and the Well’ in Roderick (1967–9) 1 72: And so they thought they’d got / A rather soft and easy thing.
[Aus]Bulletin (Sydney) 20 Jan. 24/4: Two weeks hence, Murphy meets Archer […] – apparently another very soft thing.
[Aus]E. Dyson ‘Dukie M’Kenzie’s Dawnce’ in Benno and Some of the Push 39: Mr. Dickson realised now that he had a ‘soft thing.’ It was plain that Cootie would take it lying down.
[US]Wood & Goddard Dict. Amer. Sl.
Oshkosh Northwestern (WI) 25 July 7/2: The friend of fascism is the man who loves his soft thing more than he does his country .

In phrases

have a soft thing on (v.)

(US campus) to be in an advantageous position.

[US]L.H. Bagg Four Years at Yale 48: To have a soft thing on, or the dead wood on, any object, is to hold the ‘inside track,’ the best opportunity for gaining it.
[UK]Sporting Times 18 Jan. 1: ‘Will you Bet?’ inquired Reynard. ‘Certainly,’ replied his Challenger, thinking he had a Soft Thing on.