Idiom (source English Club)

a couch potato Meaning: You can say someone's a couch potato if they're very lazy and they spend a lot of time sitting around watching TV and eating junk food. For example: Since he lost his job, Marty has become a couch potato. How can you expect to feel good and look good if you're a couch potato? If you turn off the TV, get some exercise, and eat healthy food, you'll soon look good and feel great.