Similar to a 'couch potato' but these people are lazy AND fat. Whereas 'couch potatos' are usually just lazy.
Being a slouch potato is much worse than being a couch potato.
I walked into the living room only to see my slouch potato older brother finishing yet another packet of Krispee Kremes.
You're already so lazy Jeff, if you keep eating all that junk food, you're gonna end up a slouch potato!
What a slouch potato!