- Right-click on the person's name, and select 'Remove Name...'
- Check the box next to 'Block this person' in the dialogue box that appears, and click 'OK.'
Blocking someone will prevent him or her from talking to you, and vice-versa. Blocked users can't see when you're signed in to Google Talk, and you won't see their status in your Friends list, either. If you decide you'd like to communicate with someone you've blocked, just unblock them.