What is the meaning of the word "kick in the butt"?

Definitions:

  1. a punishment inflicted by kicking the victim in the behind copy to clipboard noun
    • The kids who put toilet paper in my bushes deserve a kick in the butt. copy to clipboard
  2. an occurrence that serves as a major motivating factor copy to clipboard noun
    • It was a real kick in the butt when they lost their job. copy to clipboard