Taking this matter to a worst case scenario, eg a trial in court, anything you may have done to provoke or exacerbate it will be exploited to the full by his defence lawyer.
If, and it sounds highly likely, this character has mental health issues, this along with any antagonism on your part may well be sufficient to see him get away with it and as a result make matters worse as he could see it as vindication that reinforces his position?
It's easy for me to say as I'm not on the receiving end but maybe totally ignoring him, at least in the short term, might be the best course of action?