Knew info. I just figured this out. This doesn’t work for people responding to your responses, like a conversation thread. Only for your original stories. So far as I can tell. Also, you have to be on a PC and not the mobile app.
Scroll down to the responses to your story. The first thing you’ll see is:
Click “manage responses.” On the screen that takes you to, the drop down arrow for each individual response has the “hide this response to your story” option.
This is great!
Die, trolls, die!