Your block list is a list of players that you don't want to play with. You can add players to your block list by visiting their profile page and clicking "Add this player to my block list." You can remove players from your block list on the Manage Block List page.
Players you block list have the following restrictions:
- Any games you create with Open Seats will not show up for them on the Open Games tab.
- If they do somehow find an open game you created (such as if another player gives them the link to it), they still won't be allowed to join it.
- Any open tournaments you create will not show up for them on the Open Tournaments page, and just like games they aren't able to join it if even if they do find it.
- They will have a small "B" icon next to their name in the lobby and main game screen.
- A small "B" appears on their box on the Open Games tab and My Games page. This makes it easier to avoid games that they've joined.
- Any chat they send to a game or tournament will be hidden from view. If you want to see it, a link is provided to reveal it.
- They are forbidden from inviting you to team ladder.
- They cannot add you as a Friend.
- If they have Manager Rights within a Clan, they cannot invite you to join that Clan.
Most of the time, it is not possible for other players to tell that you have them on your block list. However, if they try to join a game with open seats that you created, or an open tournament you created, they would be notified that they can't join since they're on your block list. This is fairly unlikely though, since these games and tournaments would not even show up for them on the Open Games tab or the Open Tournaments page.
They can, however, easily check whether they're on your block list by trying to add you as a "Friend" from your profile.