Here we go.

[Vixus]

A warning would suffice for RDM?

Given the situation and context in which it happened, yes.
The Corleones had come up to our base to threaten us, stating that our turf now belonged to them and that we had to watch our backs. (We built the base near the pool area) -- That, and the fact we were receiving stray fire from across the road by the Corleones put us all on edge. The guy who according to Narcotic was RDMed had not died since the death threats (So NLR was not in effect for him), and actually was part of their shenanigans and holstered his weapon when we told him that he had 5 seconds to move away from the front gate and he did not comply and we opened fire. This is why I personally feel that it does not constitute as unprovoked RDM, but Narcotic did not fully observe the situation. I don't feel like getting in a fight over this, but this is the way it went down.

The sitting on the base wall part, I will admit that that was wrong and a warning for that really would have sufficed.

And who are you to decide on the proper punishment?

See above.