True Block

This is for a community site you administer and have moderators for?

If A is always bothering B this seems like a reasonable feature request to be able to prohibit A from commenting on B’s topics. There are some other options such as B can post in closed restricted access categories or A could be banned from the site. First step seems like should be asking A to stop posting on B’s topics, or be issued official warning to not do that from moderator could help.

Here is post in related topic about their reasoning for current structure:

If a new feature was implemented allowing members to stop any other member from commenting on their topics, seems there would be a risk of that causing additional problems.

Most important is for there to be competent moderation, so if someone has a request that someone else not bother them that will be honored. If one person is being bothered on a regular basis there are likely other people also being bothered by the same issue that needs moderator intervention to resolve.