It’s a lot simpler than that for psychopaths like Trump: it’s a simple cut that’s dehumanizing. It’s an easy way to say, “You mean nothing to me, and I know this hurts you, so I will keep on hurting you as much as possible whenever I can because I can, and that gratifies me.”
It’s one of the most effective trolling behaviors there is, because, no matter how big a person you are, it will always cut a little. And it is also one of the most obvious signs that someone is a psychopath. Because they hurt someone just because they can.
You see it all the time from trolls on the Internet.