Core or plugin? The ability to bring a person or a group's notifications to the absolute lowest with one click. I get members who say: I want zero notifications, nada, niente, zip, zippo. As a moderator I wish there was a single click that would zero out that person (or group's, but especially person's) notifications.

Ask them no click in the following link:

 

It is in the notifications settings page. 

Not sure if this stops inline notifications too.