Global mute user

I’ve come across this thread on the forum; which may be of interest to you: Discourse Shadowban
I don’t know if it works or works well. I guess you’ll have to try it.

EDIT: And if you’re just talking of ignoring a user, I understand according to what I’ve read that it’s a functionality embedded in Discourse (but you seem to need to be TL2, which I am not, so I don’t see the possibility to do it here).