I am pretty sure we covered this before but the message is not getting out. If someone puts your site in their disavow link file, it will NOT have a negative impact on your rankings.

There are many link spammers trying to get their links removed from sites and are using very threatening emails and messages to encourage those sites to remove the links. One example is in a thread at Google Webmaster Help.

Here is part of the message:

John Mueller from Google responds to the concern saying:

I love how he outright calls them wrong and then goes on and suggests they pay up to remove the link they placed on their site. It is like throwing it back in their face and using a tactic the spammer would have used.

Forum discussion at Google Webmaster Help.