Green’s Dictionary of Slang

a general term of abuse, a mean, contemptible person, one who always wants a loan.

1866		R.B. Mansfield School Life at Winchester 231: SCADGER—A Ruffian.
1883		W.M. Hardinge Eugenia 3 265: ‘Shot him?’ he said to himself, with a sort of wonder in his smile [...] ‘A pretty sort of a scadger I look, to shoot him’.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1899		J.G. Lyall Merry Gee Gee 18: I you are fastidious as to rubbing shoulders with some terrible dirty scadgers, don’t go to Stapleton’s.