I have a dog-phobic partner. My parents have talked occasionally about wanting to get a dog; when they bring it up, I remind them that if they do, I'll either visit without my partner or stay in a hotel.

So far, they've decided they like having both of us stay with them, so they haven't got a dog. But it's not a threat on my part, just a description of natural consequences. They have a right to get a dog if they want! It's their house! It won't be them getting a dog at me if they some day decide to take the plunge.