The Godfather has added an option to Mute custom messages from other players. When you mute another player, they are blocked from sending you any custom messages at all, but they can still send you the default, preset messages.
To mute another player, click on their name to visit their profile. Once there, you should see a “Mute Player” checkbox toggle in the upper right hand corner, like this:
To remove a player mute, you can click this checkbox again, or you can go to your blacklist/mute page (listed under my boss), and remove anyone you have muted there.