couch potato 
noun informal
A person who takes little or no exercise and watches a lot of television: it is no good you being a couch potato and having a Dobermann...
- By lunch-time I could hardly walk and by evening picking up the TV controller made even being a couch potato a painful exercise.
- She in turn has become a couch potato, watching old movies and ordering take out.
- Instead of just sitting in front of your television being a couch potato, it offers you opportunity to shop online, play games and enjoy other activities.