That is what they are supposed to do, so it is not an immediate threat. 

The real threat is the $200 trillion in unfunded liabilities and $20 trillion in national debt.

(Let them imagine the possible other options or consequences)Up until now, I think they feel they've had the "upper hand" in the situation, but I have to believe that self-preservation and the threat of legal consequence might be motivators enough for them to be reasonable.  

After several threats of the tenant wanting to take me to court (for not selling him the property) his attorney advised him he had nothing to go on for his counterclaimBased on this a court date was then postponed (after I was scheduled to fly into the state where the property is located) and then a second court hearing postponed due to a deal being struck out in the pre-trial conference.

I'm not worried about the threat, but wonder if there are other rules for roommate situations, where it is acceptable to stand on criteria of not accepting a dog.

This cranky old lady targets single women, tried to run me over with her car, screamed and made threats to me at a hearing (over one of half a dozen issue that were  "accidentally" sent to me) I have had to pay over $2000 in fines just to appease my landlord while I file harassment, libel and defamation claims against her..She has refused to provide my LL with the videos (of course) that show her doing her crazy acts, so, Im taking her to task.

Hi @Priyanshu Adathakkar and @Adam Adams, The threats to Section 1031 of the Internal Revenue Code ("1031 Exchange") tend to surface every 3 to 5 years.

Hello BP, I hired a contractor for tile & tub installation in my 2 bathrooms. It was part of a water damage claim so the insurance company is involved. The initial proposal I got from the contractor was $7000 doll...

They can't just invite any friend, that new roommate needs to go through the proper channels and be screened.Assualt / Threat:  If the tenants indicated the ex-roommate was abusive or threatening, do your best to resolve this situation quickly. 

(Other than looks or threat of collapse.)