My nice 37+ rating (earned over 2-3 years) turned orange -1 without having ever had business with that "man" immediately.
Your rating was 0.
None of the users that have left you positive ratings are part of the default trust system (depth 1 and 2), therefore their ratings don't affect you score unless you have a custom list (which seems to be the case here).
Remove them from your trust list or put a "~" in front of "Default Trust" in your trust list and their ratings won't count toward your score.
That's what I'm reading from Lauda's comment here (from another thread).
Oh, and don't do anything to earn negative trust. But with that said the trust system, while good for trade transaction decision making is completely subjective and frequently abused in non-trade scenarios. If someone doesn't like the cut of your jib they can just leave you a bad trust rating and its there forever without any consideration for whether it's accurate or vindictive.
If people take your comments out of context they can leave you negative trust AND put a value on it that's completely made up (or at best exaggerated).