If your mouth has gone cracker dry from excessive whistling, and you've dislocated both shoulders with your flailing-gone-wrong, you may have to resort to the Sexy Leg. Pioneered by Baby Boomer hitchhikers, hiking up your skirt and showing some skin is a last ditch method to getting someone—anyone—to give you a lift.
Make sure you have the cherubic, hairless gams of David Beckham if you're going to even attempt this technique. Using cleavage is always a bad idea though. You want the driver to pull over, not distractedly crash into a newsstand.