At least from the user side, there is a procedure that hasn't been listed yet: following the link to mathoverflow.net/contacthttps://mathoverflow.net/contact and contacting support with "I want to report a Code of Conduct violation". This is, as far as I can tell, the procedure most clearly dedicated to preventing harassment.
I don't know how these "contacts" are handled on the moderation side, and would appreciate elaboration from someone who does.
