Was wondering when this would come up. Short answer: no, you can't hide all posts from another forum member, but you can mute all notifications from that user (say, if they reply to a topic you've posted in or similar). Set it up in your user profile.
Long answer why you can't hide all posts from a user straight from the Discourse founder here.
Edit to add: if you have a problem with what a user is saying and think it violates the community guidelines, flag it and we'll follow up.
I've disagreed with many people on the internet and hope to disagree with many more, but keep in mind that this is the internet - everyone has an opinion, but yours is stupid.
Relevant webcomic link.