It's best to mute the longest unique string possible. Blocking/muting from "GM" through "wss://", (and the exact characters in between) will give you optimal results until the message changes.

In Amethyst, the name can be blocked the same way, so anyone with "replyguy" (or is it "reply guy"?) in their name will be blocked. I don't know if Primal et.al. can block names, but it's worth a shot!