Hi serafimetal,
We had to do this just recently, one of our friends trampled our boundaries. We emailed the person to never come near us or contact us again.
You've got to protect yourself, we'd never had to do anything like this before either, but fortunately we shot off several emails in the heat of anger
Now all we have to do is keep stopping ourselves from emailing any kind of suggestion that we might accept an apology, it's hard if you trusted them before.
Lucy (protector)