Cantankerous, I've been in the same situation. And it's especially annoying when a member of the opposite sex assumes that you're JUST DYING (not!) to talk to them.
I agree with PSquared. You just beat them at their own game. Why should you go out of your way to talk to someone who won't even look at you. Ignore them back, ignore em harder. Don't ask how they're doing, don't say good bye, don't say hello. Just walk by them as if they don't exist.......as if they are as invisible as AIR. Once they get the message that you don't have the DESPERATE DESIRE to talk to them..........they might approach you and start being nice/talking to you. I say, be polite and cold to them. Let them know that you are not into playing games. And you don't care to deal with people who ONLY talk to when it SUITS THEIR MOOD! And if that's the case, they can their self-centered self-righteous company elsewhere!