I recently quit my job, after a three months notice, and I've changed my region of residence (it's like moving to another state in the USA, but the regions are smaller).
The last day, when everyone was saying goodbye all along the day, one of them (I thought we were close, but we stopped talking 9-12 months earlier, even though working in the same Open Space) proposed me to stay in touch (like some of my other co-workers did).
I don't have any interest in maintaining this relationship. Nine to twelve months ago I discovered that it was a toxic "friendship" (she was manipulative with me and it was a one-way/asymmetric friendship). I would try to talk to her to fix it, she just laughed and accused me of being a child; she seemed angry/annoyed. We didn't talked since then. She was generally warm and nice in public but in private, either she was charming, authoritative or pushing on my weaknesses when she wanted something; or she was just judging or depreciating when I was opening up.
After a bunch of compliments, she gave me her e-mail address, telling me to use it, to which I answered: "I won't use it".
Thereafter, I think that it was a bit harsh (passive-aggressive). Was/is there a softer (and not too long) way to turn her proposal down?