not that anyone's broken it, but the biggest rule on cohost is: if you share my posts you must not include an inane comment. it has to be interesting or funny or thoughtful. never inane
Cohost Tip: if someone annoys you, you can go to their profile and use the "silence" option and you will never hear from them again, without incurring the interpersonal and psychological ramifications of blocking them. You can use this to curate your notifications feed and timeline.
You can also silence posts, which is useful if you make a post that blows up (I had to do that with the "cohost tips" post) or if someone makes a reply that blows up
Edit: as @NireBryce mentions,, you can also use that private notes field to keep track of why you silenced or blocked someone, note that they've been weird to you in case it comes up again, note that they're cool, or whatever you like
Edit: also important: per @xkeeper's note,, note that follows and blocks work on a page by page basis, so that people can't determine what pages belong to the same person. Private notes are account-wide.