The people I am spiteful toward are no longer in my life. I don't keep people in my life who are toxic. When I say spiteful, I do not mean that I act in a spiteful way toward them. I only fantasize about it occasionally.
Healthy? I would say not. As the Buddha said, holding on to anger is like picking up a hot coal with the intention of throwing it at someone else. You are the one who will be burned. However, I have not yet had the control to excise my negative feelings. Since I only experience them during the rare times when a memory of the person or event occurs to me, I don't consider it one of my bigger failings.
Ooh, here's something spiteful. A few nights ago someone hijacked my email account. They used it to send a virus to random people in my address book. I sent out a follow-up email warning everyone not to open the link--with the exception of my ex-husband. And I wouldn't be at all sorry if his dumb @ss clicks it.