1. noun. Reffering to the Jim Henson character from Sesame Street. Any person often reffered to and talked about by a single person or small group of people, but who has yet to actually show up anywhere that you and/or most people you know have ever been, often creating doubt as to whether this person actually exists.
2. adjective. Having charachteristics of someone often reffered to and/or talked about, but who one has never met or never seems to actually be present, and possibly may not even exist.
1. Alexis has been talking about her boyfriend Byran for over a month, but I think he's a "Mister Snuffleupagus".
2. I think this guy you keep talking about who supposedly has the best shit in town for cheap is totally Mister Snuffleupagus, dude.