@jenniferplusplus @hipsterelectron Mechanically, "rejecting a reply" is just refusal to include it when a request for the replies/thread is made, pretending it's not there.
If you do that, only users whose home instance is the same instance as the unwanted reply-guy is replying from might be able to see the reply.
Adding something to the protocol to ask that instance not to allow it is the main addition that would be nice.