BLACKGUARDLY
rascally, roguish, scoundrelly, blackguardly
(adjective) lacking principles or scruples; “the rascally rabble”; “the tyranny of a scoundrelly aristocracy” - W.M. Thackaray; “the captain was set adrift by his roguish crew”
Source: WordNet® 3.1
Etymology
Adjective
blackguardly (comparative more blackguardly, superlative most blackguardly)
Characteristic of a blackguard.
Source: Wiktionary
Black"guard*ly, adv. & a.
Definition: In the manner of or resembling a blackguard; abusive;
scurrilous; ruffianly.
Source: Webster’s Unabridged Dictionary 1913 Edition