From time to time you may run across bothersome or offensive people, or other kinds of 'unwanted contact'.  When that happens you can 'block' them from further contact.

From your Pal List
To block someone that you already have on your Pal List, just right click on their user name in your Pal List and select 'Block this Member'.

Within a Group
You can block anyone in a group so they can't contact you anymore.  Just right click on their user name and select 'Block this Member'.

When in a chat room you can also 'ignore' people.  If you ignore a person, you won't hear them when they speak, or see anything they type.  If you are in a room and have 'ignored' someone who is frequently 'on mic', you may experience long periods of silence where you would have otherwise heard them speaking.