If you want to prevent another Monster Owner from contacting you:
   

1 -  if they've requested to be your friend.

Click X to deny their friend request : 

Then click the BLOCK button : 

2 - If they're already on your Friends Tree

click the BLOCK button to block them from contacting you in the future : 

Click Yes :

TIP :  Clicking DELETE will delete the person from your friends tree, but they can send another friend request. Only BLOCK will completely block them from contacting you again.

SAFETY TIP : If anyone makes you uncomfortable, report them straight away by reporting their pinboard post (just click the "M" button)
  

Then click Yes