Kick the Dog/Theatre

Stephen Sondheim's Assassins: Sarah Jane Moore shoots her dog for barking, then stuffs the dead dog in her purse—but it's played for laughs. As far as marking her as a credible threat goes, Sarah Jane's real Kick the Dog moment is when she turns her gun on her infant son, because he wanted an ice-cream. Thankfully, she doesn't pull the trigger.
Shakespeare's character Iago in Othello, encouraging the evil deeds of his henchman Roderigo: "...drown cats and blind puppies..."