Green’s Dictionary of Slang

josser n.3

also jossy
[? Polari josser, an outsider]

a simpleton, a fool; a victim for criminal gamblers.

[UK]Swell’s Night Guide 114/1: Ben, a sam, a green, a jossy, a soft fellow.
[UK] ‘’Arry at Stonehenge’ Punch 28 Aug. in P. Marks (2006) 85: Dry up, you old Josser.
[UK] in Punch 26 Nov. 252: Shut yer face, you pattering josser!
[UK]Wincott & Elen [perf. Gus Elen] ‘Down the Dials’ 🎵 And if the josser finds the card, we bangs him with a brick.
[Aus]Sydney Sportsman (Surry Hills, NSW) 11 May 2/3: [W]hat the silly josser wanted to defy the electric disturbance for does not appear.
[UK]Magnet 10 July 8: Silly josser!
[Aus]Sport (Adelaide) 22 Jan. 5/3: You can bet on these jossers [...] /They will always drink grog.
[US]E. O’Neill Bound East for Cardiff (1923) 6: That silly ol’ josser! Wot the ’ell would ’e know abaht anythink?
[UK]A. Christie Secret of Chimneys (1956) 19: A josser like myself from the backwoods of Canada would be making all sorts of bloomers.
[UK]M. Forrest Hibiscus Heart 93: Didn’t know old Gordon, silly old josser, was a bird fancier.
[Aus]Mirror (Perth) 6 Nov. 12/3: You old josser.
Wright & Eplett [perf. Gus Elen] ‘’E don’t know who 'e are’ 🎵 Which shows the josser don’t know where ’e are.

In derivatives

jossey (adj.)

foolish, gullible.

[UK]T. Woottwell ‘The fces I’ve Seen’ 🎵 There's the bookie black with shouting odds at double barrelled force, / ’Til he makes some jossey backer put his money on a nacker.