sit on (one's) butt

sit on (one's) butt

To be idle, especially when action is needed. You can't just sit on your butt all summer. Get a job, join a club—do something with your time! I was tired of sitting on my butt while so many people in the city needed help, so I decided to join a homeless shelter and try to lend a hand where I could.
See also: butt, on, sit