The phrase "couch potato" is used to describe someone who spends a lot of time sitting or lying down, typically on a couch, watching TV and not participating in physical activities. Full definition
For example, if you are a very active person who loves hiking... you don't want a lazy coach potato dog.... (brunetteinred.com)
These pooches are more likely to linger on the coach than run around in circles looking for something to do, which makes them a good choice for coach potato owners or simply those who prefer calmer personalities. (notinthedoghouse.com)
Many owners describe their Greyhound as the «45 mile per hour coach potato.» (pethealthnetwork.com)