When a automobile begins to accelerate before it is prudent. Most often witnessed at intersections that are controlled by traffic lights when a driver incorrectly assumes that it is his turn to go next.
Driver: Look at that guy raring to go. I'll bet he doesn't know that it's my turn to go next.
<Car in question moves about a foot and then stops abruptly as he realizes his light did not change green>
Passenger: How embarrassing; a classic case of premature acceleration.