A suite is a set of rooms that contain furniture. A couch is a piece of furniture that multiple people can sit on. Suite and sweet are homophones. Sweet is a descriptive word used to describe the taste of something, typically if that something is sugary. If someone has a "sweet tooth" it means they really like and crave eating sweet things. The joke is centered around the word suite and its homophone sweet. 
I met a man who loves eating couches . I think he has a suite tooth .