"To immediately exit out of facebook when a "friend" you do not want to chat with (or know you are online) pops into the chat window."
I have a few facebook friends who are nothing more than old acquaintances, and I should have really thought twice before being their Facebook friends (ie. people I never want to see again). Whenever they come online to Facebook and appear in the chat window, I have to face-book before they know I'm on too.
Oh damn, Mark just logged into Facebook and is on my chat screen. I gotta face-book before he sees me online.