Green’s Dictionary of Slang

on doog adj.

[backsl.; on adv.2 + doog adj.]

no good.

[UK]H. Mayhew Great World of London I 5: It’s on doog, Whelky, on doog (no good, no good).
[UK](con. 1840s–50s) H. Mayhew London Labour and London Poor I 23/2: On doog ... No good. [Ibid.] 24/1: He [...] concluded emphatically with ‘doog:’ — ‘good’.
[UK]Sl. Dict.
[UK]J. Franklyn Cockney 298: A few stray words and expressions, such as top o reeb (pot of beer) and on doog (no good) survive with restricted usage in cockney colloquial slang.
[Aus]R.G. Barrett Davo’s Little Something 13: If it [i.e. a piece of meat] was completely rotten and crawling with maggots, it was ‘on doog — luff of toggams’.