Green’s Dictionary of Slang

shab n.

an unpleasant, sneaky person.

1637		Bastwick Litany I 19: Neither are those Shabs for any merit in themselues [...] worthy to giue guts vnto a beare .
1735		Dyche & Pardon New General Eng. Dict. n.p.: Shab A mean, sorry, pitiful Fellow, one that is guilty of low Tricks, &c.
1744		Dyche & Pardon New General Eng. Dict. (4th edn).
1827		Egan Anecdotes of the Turf, the Chase etc. 209: See tight-lac’d Shabs, ape tip-toe Coves.
1839		‘Jim Crow in London’ in Jim Crow’s Song-Book 8: Respectables all keep a gig, / But all the vulgar shabs, / Drive about the Lunnun streets, / In patent safety cabs.
1851		G. Borrow Lavengro Ch. xcviii: ‘Any name but that, you shab,’ said Black Jack.
1885		Bulletin (Sydney) 21 Mar. 14/3: They don’t begin to know what sport is. They are just ‘shabs.’ Not all the Bulletins or other journals in the world could shame such scum.

In derivatives

shabster (n.) [-ster sfx]

an unpleasant, sneaky person.

1890–1904

Farmer & Henley Sl. and Its Analogues.