How can I censor or noplay someone? I don't want to listen to their tells or get challenges. (ICCforMac/Windows)

Shortcut for censor(which includes noplay):
Place your mouse-cursor on the player's username (Shown in blue in a channel/chat console, in a game console or showing in the list of players in a channel) and right-click on it. A pop-up list opens where you  select  'Ignore Messages and Challenges From This User'.

 
You will follow virtually the same process to remove a player from your censor (which includes noplay) list, except you will choose 'Allow Messages and Challenges From This User'.

Command Line Method for Censor and Noplay:
Open your console by clicking on the Console Icon on the bottom of your screen or menu above: View > Console.

To add a player to your censor list, type: +censor username in the command console.  Example: +censor Fred
To remove a player to your censor list, type: -censor username in the command console. Example: -censor Fred
Type: =censor  to see the players currently on your censor list.

For noplay you can use a similar system.
+noplay username
-noplay username
=noplay

Censor will eliminate all communication from that player and  it will block players challenging you or accepting your seeks. This will have no effect if you play in tournaments, 1-minute, 3-minute, 5-minute, 15-minute, 45-minute or 960 pools.
Noplay will only block players challenging you as explained in censor.

For more information read "help lists" and "help censor".

For information regarding reporting abuse read  "help Complain"