Maybe because this is the first time someone has threatened to sue me.

We have threatened to call Department of human services on the conditions they had their children in.

the issue here is if a tenant is threatening  a lawsuit your next step is not to talk with them but to respond such as.

I'd personally hold out for cash for keys.Anyone here thumping their chests about how they'd threaten their tenant - put yourself in their shoes. 

Yes you can try and force them to pay based on the lease, and even threaten them, probably won't do any good though and only cost you time and money.

I've seen tenants blackmail their landlords and threaten to turn them in to the City's Code Enforcement when they don't get their way.

Tenant now is threatening to "talk to his lawyer" for the pain he / his family (wife + baby) have been through, and that he is "collecting the evidence". 

At this time, the plumber (now his wife joined the conversation) became irate and cussed out our property manager, even threatening bodily harm to him.

You're spending a bunch of time dealing with bizarre problems, and then eventually they are demanding to be let out of their lease because of mold or threatening to contact the city because the unit isn't habitable - when if they were just on a M2M, they'd simply give notice to move out.I get the idea of trying to time your leases so people won't move out during the winter, but there's not guarantee a tenant won't need to move then, anyway. 

Now he has sent the PM and Us a threatening letter to take us to court over his security deposit and damages.