Is there any way of blocking a player?
Click on any name and select “block”.
You will be presented with two options, to either block messages, or to block him/her from accepting your games. You can chose either or both, but note that currently there is not any implemented way (while there is a workaround) to view all the users you have blocked, so reversing the block can be problematic if you do not remember the username or have blocked a lot of players.
So just make sure you mean it I guess