you can block invididuals, and turn off replies, but its often not effective, because if you go back to the orignal convo you blocked, you can see them bitching that you blocked them, oh and they created another account so they can evade your own block(since they cant join your convo thread in a subreddit. often times they will retaliate by reporting you for blocking them. and risking reporting them, can put you at odds with a mod, say you cant make too many reports.