Synonyms for Sadistic:

adj.

cruel, perverted (adjective)
vicious, brutal, perverse.
wicked (adjective)
damnable, improper, blameworthy, evildoing, immoral, obnoxious, iniquitous, felonious, depraved, debauched, perverse, corrupt, Misdoing, reprehensible, indecent, scandalous, villainous, wicked, bad, sinful, criminal, lawbreaking, debased, shocking, degenerate, base, black, wrongdoing, sinister.

n.

pitiless, monstrous, unkind, hateful, awful, hard, evil, uncharitable. cruel (noun)
vicious, brutal, cruel.

Other synonyms:

inconsiderate
unkind.
vicious
cruel.
Other relevant words:
evil, cruel, brutal, pitiless, vicious, unkind, monstrous.