A, "Katie", is the ultimate underage party girl. A young lady that is over 18, but under 21, yet doesn't let that keep her from getting into bars, clubs, and other situations where debauchery is likely to occur. "Katie" is often subjected to the walk of shame after a night of festivities, yet this won't stop her from going hard in the paint.
That girl in my economics class is the biggest "katie" on campus.
I always see "katie" walking down Franklin street with a different dude every night.