@ Lola Sylvian - This thread is for reporting Forum related issues, as explained in the first post. There is nothing that the F Mod Team can do about in-game situations.
If you come across someone breaking the rules in game, then you need to use the in-game Report Feature at the time of the incident. That is the only way to send Jagex the evidence they need from their own systems to be able to take action. And the reports are also useful to establish that it is a pattern of behavior, rather than just a one-off joke with a couple of his friends. When he says that a J Mod friend will get him unmuted, then report that as well.
If you have evidence, rather than just rumors, of this player being a serious threat to the community, you can also send that to Jagex using the [email protected] email address.