Green’s Dictionary of Slang

(US teen) in a totally unacceptable manner (on the basis of a group’s standards).

[1905		F. Hutchison Philosophy of Johnny the Gent 60: ‘He hung a big eye on him an’ just walloped him somethin’ scandalous’].
1997		G. Sikes 8 Ball Chicks (1998) 32: ‘This girl was behaving scandalously.’ Gang lexicon reserves the word ‘scandalous’ for the most amoral act.