I assume you mean blocking a specific post from being seen rather than blocking the user who posted it because in the latter case you can use the three dots to the bottom right of a post. As far as I am aware there isn't a way to block specific posts at all? Do tell if there is.
I think a good implimentation would be keyword filters but the ability to conveniently remove posts from our feeds without seeing them would also be great for those of us who are more content sensitive. You should make a request on the github page.