Green’s Dictionary of Slang

(US) an observer, a non-participant.

1901

‘Hugh McHugh’ John Henry 65: From the moment you reach for your cue the sofa-pounders cut loose and chin you to a call-down.

(US campus) someone who lies around doing nothing.

1984		Pantagraph (Bloomington, IL) 18 Feb. 33/1: Sofa spuds lovin’ the tube.
1987		Birmingham Post Herald (AL) 1 Dec. A-5: I am speaking of those maligned people known as couch potatoes. Or if you prefer, sofa spuds.
1987		Eble Campus Sl. Spring 7: sofa yam – someone who sits on the sofa all the time doing nothing.
1994		Newcastle Eve. Chron. 16 Apr. 25/2: [headline] Telly Heaven for Sofa Spuds.
1996		Eble Sl. and Sociability 31: Sofa spud ‘person who lies around doing nothing’ alludes to the well-established couch potato. [Ibid.] 70: In the late 1980s and early 1990s, the nationally recognized couch potato for ‘someone who lies around doing nothing more energetic than eating and watching television’ was still in use, along with its synonymous offspring sofa spud and sofa yam.
1999		Gazette (Montreal) 16 June 148/2: Dedicated sofa spuds simply have to grin and bear it.
2001		Dly Oklahoman (OK) 13 July 58/1: Exercise tones the blood [...] blood of inactive people is too thick [...] ‘sofa spud’s blood’.
2009		Dly Oklahoman 2 July 56/1: I’m not just your ordinary run-of-the-mill sofa spud. I’m a connoisseur of couch potato technique.

of a homeless person, living with a succession of friends and sleeping on their sofa.

1998		Juliete Torrez [bk title] The Sofa Surfing Handbook: a guide for modern nomads.
2004		P.W. Lunneborg Women Police 76: One poem was entitled ‘Sofa Surfing,’ how this gal went from one sofa to another.
2012		‘Radical Rooney’ A Year on the Streets 480: Before Pete moved he was sofa-surfing at Connie’s.
2023		N. Gerrard in Guardian 9 Dec. 🌐 Women are the hidden homeless [They] sleep in disused cars; have ‘survival sex’, such as sex work or sofa surfing in return for sex.