Is there a way we can BLOCK someone on the Board, and not see any of their THREADS/COMMENTS

Currently the boards does not have features like this, and Riot can't really spare the resources for boards development while they're working on the Client Update.

However, there is a third party option called the Forum Enhancement Kit (FEK). This provides many useful extra functions to the boards, including blocking a player to hide all of their posts. This is developed by Tundra Fizz, one of our own, and is used by many Rioters; the script is open source so you can see everything in it and edit it so we know it's safe to use.

We really need this.

Seconded.