Green’s Dictionary of Slang

(orig. US) to speak without expression, esp. in a situation that would normally demand some emotion.

1937		J.M. Cain Serenade (1985) 310: If she had dead-panned, I think I would have sat there and taken it. But she didn’t. She laughed.
1947		N. Algren ‘Depend on Aunt Elly’ in Texas Stories (1995) 111: He dead-panned her and shifted his eyes just a little.
1960		E. De Roo Big Rumble 27: ‘Hi, Claw, how ya doin’?’ Twitch asked him. The others dead-panned.
1967		(con. 1951) McAleer & Dickson Unit Pride (1981) 6: He gave me a fishy look but I deadpanned it.
1979		E. Torres After Hours 120: Rutledge dead-panned it.
1986		C. Hiaasen Tourist Season (1987) 5: ‘Is this the Pan Am terminal?’ he deadpanned to the first secretary he saw.
1990		(con. early 1950s) J. Ellroy L.A. Confidential 136: The fruit deadpanned him cold.
2000		Indep. Rev. 23 Feb. 11: Leight deadpans with regard to the hunk factor.
2023		(con. 1962) J. Ellroy Enchanters 211: BVerlin reacted. He deadpanned the ‘Perloff’.