Denied.
This was not RDM, as he had a PK approved on you by a member of UA.
Additionally, Slickb's actions in response to you breaking NLR and metagaming by returning on another character Immediately after being PK'd and attempting to confront those involved with your PK is fully justified.
Given the circumstances, I see no issue with his response and no action will be taken against him for that.
Since you've already submitted a PK appeal, that is where your PK will be reviewed by a member of UA.