Yes, I know. Tried out, but what does -2 mean? Bad rating by vip or similar?
You should read up on how trust works. There are DT1 and DT2 members who are trusted by "DefaultTrust" and DT1 members, respectively. Each user by default has DefaultTrust in their trust list and that is why DT1 and DT2 ratings are the most impactful.
A -2 trust means that a DT1 or DT2 member has given red trust to a user (or you). Note that this is only for users who have yet to modify their trustlist.