Fast fix - block your *unwanted* contacts from Google Chat
Click on Contacts on the left side of your Google page.
Then, select the person you'd like to block. When you click on their name a window will open and you will see a "Show in Chat List" drop down menu. You can select from Auto, Always, Never, and Block.
Since in this instance, I'm cleaning out my chat list, I would select Block for this contact, and poof, they will automagically disappear from my Chat list. If you make a mistake or you want to put them back on your list, you can just select their name and then click on Auto or Always to get them back on the chat list. 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. (No offense Leonie, BFF)!
If you don't want Gmail to automatically enable chat privileges with your contacts you can go to Settings
Then click on Chat,