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1.
Any driver who becomes oblivious to others (in all senses), and oblivious to other externalities such as speed limits, lane drifting, oncoming traffic, pedestrians, bicyclists, traffic signals, parallel parking, parking within the lines in a parking lot, backing up, and most often four-way intersection. 
Priusing is often the result of a misguided sense of what is right and good for the world.
The driver brought to the point of Priusing has typically led a life of floundering hope and preaching convenient yet incomplete concepts of ancient teachings. They can often be seen basking in their own self glory, to busy to realized their impact on others.  
A driver that is in the act of Priusing would never realize they were hindering the mobility needs of other drivers.  For example, a person Priusing would drive noticeably slower in the fast lane on the freeways. If confronted with that fact, they would curiously deny that act and say something like, whats the hurry anyway? Priusing is further illustrated by an astonishing lack of understanding of how labor intensive the very progress that the Priusing driver condemns, yet enjoys. These driver are most often found driving a Prius and are routinely poorly dressed. 
Why are we going so slow?

The guy up ahead is totally Priusing.

Why did two cars go throught the four-way intersection?

That driver was Priusing.
by Stinky Observer June 10, 2013
 
2.
Verb - The act of driving a Toyota Prius. To Prius is to choose to drive a Toyota Prius over another vehicle with equal or lesser gas mileage. Most commonly used in reference to a daily commute.
Did you take the S5 today so we can take it to lunch? No, I am Priusing.
by JCeezle September 01, 2011