If someone come to your account and he give you a negative feedback for nothing, what you gonna do ? you will give him the same i bet.
Giving retaliative feedbacks doesn't solve the issue, it might make you feel good but it doesn't solve anything. Untrustworthy feedback (from non DT members) are as good as useless especially as it doesn't affect your profile or reputation (on the forum) unless, your trust page get viewed. If you think a users is abusing the trust system (multiple abuse and not just on your account), you can bring such cases opening to the public and that user might get what he/she deserves.
Hardly before you see any user doing something right not get a false feedbacks. So from my point of view, if you get a false feedbacks that doesn't affect your account, you let it go and continue your activity on he forum.
He is in DT2, due to some inclusions from a DT1. I see it under trusted feedback on OP, I am using default trust list FYI.
Thanks, just notice it also from using the default trust viewing option. Hope he resolved the issue soon.