How can I block someone in Google Chat/Gtalk?

Ah yes, one of the greatest liabilities of the digital hyper-connected world we're in is that not everyone out there wants to be friends with you in the same way you want to be friends with them. Not so good. Sometimes it's annoying, and other times it can be far worse - or creepier - than that. It sounds like you're in the latter situation, and it's not good.

The trick is that it sounds like you want to remain available to your friends rather than just shut everything down completely. If you did want to just become invisible, there's a setting in Gmail itself that lets you permanently cloak your presence. I'll show you that first, but then I'll show you a better way where you can pick that individual and simply block them from chatting with you.

First things first. Log in to Google Gmail and then look on the lower left side of the page. You should see something like this:

Click on the little "+" icon and it'll open up, showing you whom of your Gmail contacts are online and available to chat:

If you'd like to become invisible to everyone, see where it has your own status and adjacent to it a little downward-pointing triangle? (my status here is "available for text ch" [short for "chat"]) Click on it and you'll get a pop-up:

Choose "Invisible" and you'll forevermore be invisible to people who are on Gmail and no-one will be able to chat with you because they won't see you.

Let's presume, however, that you don't want to stop your real friends from saying hello, just block the creepy guy. To do that, find them on your chat list and move the cursor over their name. After a second or two, a bunch of options will pop up:

Click on "Video & more" and it will show you a list of additional options:

That's it. They're blocked. Now, when they see you on their contact list, it won't give "chat" as an option, as I see when Ed (who has blocked me!) appears on my own list:

If you have a change of heart, you can type in their email address into the contact box and it'll give you the option of unblocking them:

That should do the trick for you. Good luck with the situation.