I think the best and least expensive thing you can do is go see a local attorney and ask him or her to write a letter to the guy, warning him that you may sue for defamation and other causes of action. Probably you should talk with your boss as well, explaining that this enmity (which he clearly has witnessed) is disruptive of the work environment and you should request that he tell your co-worker to either quit it or to quit.
Good luck to you.
Michael S. Haber is a New York attorney. As such, his responses to posted inquiries, such as the one above, are limited to his understanding of law in the jurisdiction in which he practices and not to any other jurisdiction. In addition, no response to any posted inquiry should be deemed to constitute legal advice, nor to constitute the existence of an attorney/client or other contractual or fiduciary relationship, inasmuch as legal advice can only be provided in circumstances in which the attorney is able to ask questions of the person seeking legal advice and to thus gather appropriate information.
Good advice from my colleague. Don't give this guy what he wants by giving him a reason to call the police. And do speak to your boss (or HR, if you have an HR department) about this guy's intereference with everyone getting their jobs done.
If you do want to hire a lawyer to threaten him with a defamation lawsuit, these defamatory statements need to be provably false facts, and not negative but true or mostly true facts, and not opinions. You may be better off just ignoring this guy, if you can.
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