@MrMcNasty I don't know how that makes her not malicious. And given her behavior, it would not be at all surprising if she held the same disdain towards the rest of humanity as she does to the protagonist.
Given the sheer number of human beings, past and present, it would be extremely improbable if not outright impossible for no other person to have similar thoughts as he did in seeing death as nothing more than a means to an end. But Death herself has already said that the protagonist is nothing special in thinking that way, and it was just really bad luck that he caught her attention on a bad day.
If we use your ant analogy, with every human being an ant, and the protagonist's dismissive opinions on death being an ant bite, Death would be covered in ant bites, and yet she only decided to single out one ant out of the vast number that bit her. And unlike most people, she didn't just kill the ant and move on with her day, she chose to torture it for that single bite.
I wouldn't be surprised if it turns out that she's done this to other people in the past, actually. But that doesn't change the fact that she's a petty and cruel bitch for doing something like this.