adjective

wilfully causing pain or suffering to others, or feeling no concern about it.

people who are cruel to animals

brutal,savage,inhuman,barbaric,barbarous,brutish,bloodthirsty,murderous,homicidal,cut-throat,vicious,ferocious,fierce,wicked,evil,fiendish,devilish,diabolical,heinous,abominable,monstrous,atrocious,vile,hideous,ghastly,nasty,spiteful,mean,callous,sadistic,ruthless,merciless,unmerciful,pitiless,unsparing,unrelenting,remorseless,uncaring,unsympathetic,uncharitable,heartless,stony-hearted,hard-hearted,cold-hearted,cold-blooded,bloodless,unfeeling,unemotional,unkind,inhumane,severe,harsh,stern,inclement,flinty,draconian,beastly,dastardly,sanguinary

verb

spoil or ruin (an opportunity or a chance of success).

Ernie nearly cruelled the whole thing by laughing