When the young guy renting the house had a minor difference with his girlfriend he threatened to slit her throat. 

This should not threaten him.  

I had to hire another subcontractor to come in and fix the previous subcontractors work and finish the job.Now the first subcontractor is threatening to file a lien on the property.

He is saying it wasnt acceptable to have his son sign and is threatening to "go to the authorities".

He is threatening to sue me for mold that damaging his health but at the same time he will not leave!

If he threatens you, I would file for an order of protection and no contact.

My evicted tenant will not stop harassing me, threatening me, and trying to blackmail meI have made some huge mistakes and I'm trying to climb out of this hole.

I had to request my real estate agent call their agent and threaten to pull the deal and if they went after my earnest money the possibility of reporting fraud. then magically the required documentation showed up the next day and the sale closed in a week.

.) - Was passively hinted at being sued by one tenant, and explicitly threatened to be sued by a former tenant - Had 2 tenants cancel their leases early - Plunged someone’s crap out of a toilet in my Airbnb unit (never again!)

You're going to threaten your reputation for that.If this guys has a ax to grind with you, he could look up every tenant right and law and be anal with you, and cause you real headache.