Don't you love drivers who'll pass from behind just when a vehicle is bearing down in the opposite lane? Jeez, can't that guy wait five seconds till there's room to swing around? Nope -- he'll squeeze by and cause a three-abreast situation with two cars and one nervous roadie.
There's no way to prevent this, unfortunately, but at least there's a way to know it might happen.
Watch the oncoming car. Its position will tip you off when there's a dope about to pass.
If the oncoming driver starts hugging his edge of the road, that's the signal. If he also brakes, it's a red alert. Be on the white line and ready for a tight squeeze. Quickly check for an escape route off the pavement, and take it if you feel the need. Better safe than a hood ornament.
By watching oncoming cars this way, you won't have to be so concerned with what's coming from behind. Those cars will tell you, removing the need to glance back and risk a swerve at exactly the wrong moment.
It's a shame that some drivers aren't more considerate of cyclists. You can lessen the risk on squeeze plays by always riding a straight line no more than 18 inches from the road edge.