Interesting thread, I like the advice about looking in certain places, like the bridge of the nose or the corner of one eye. Sometimes I get, I don't know, almost mesmerized by things--like if a friend is wearing a sparkly necklace I have trouble not looking at it when we're sitting across from each other at lunch. One thing that works for me is acknowledging the thing I'm staring at in conversation, then moving on--like, "Oh, your necklace is so pretty, I just keep looking at it." Then I make a concerted effort to not be drawn back in by it.
Other times, I must admit, my eye is drawn by something that seems weird or ugly to me, especially if the conversation is kind of dull. Like, sitting in my boss's office, listening to one of her monologues, becoming more and more convinced that the thing on her shoulder is a small bug... At which point, I try to either more actively engage in the "conversation," or maybe even say, "Sorry, can I interrupt for second, what's that thing on your shoulder? Oh, I thought it was a bug."
So my strategy is basically to realize I'm staring, and then force myself to look elsewhere, possibly with acknowledgement of what had gained my attention, because that seems to help break its hold on me. You know, as long as it's not something like, "Sorry, I was mesmerized by your cleavage."