Green’s Dictionary of Slang

(orig. US) a weak, effeminate man.

1938		R. Chandler ‘The King in Yellow’ in Spanish Blood (1946) 80: Cheap spenders [...] pantywaists with silk handkerchiefs ’stead of neckties.
1940		W.R. Burnett High Sierra in Four Novels (1984) 347: I was just ashamed of myself for being such a panty-waist.
1952		Lait & Mortimer USA Confidential 182: Quigg is now playing for the mass audience, a panty-waist who speaks liberal and bends left.
1967		W. Murray Sweet Ride 206: No, these bleeding hearts and pantywaists tie their hands.
1970		San Diego Sailor 2: I wasn’t going to play pantywaist either.
1986		Eble Campus Sl. Nov. 6: panty waste – loser.
1989		H. Rawson Dict. of Invective (1991) 282: pantywaist. A sissy or coward.
2004		J. Ellroy ‘Jungletown Jihad’ in Destination: Morgue! (2004) 334: He vibed parasitic pantywaist with molten mean streak.
2017		Twitter 21 Aug. 🌐 Ignore all those pantywaists telling you not to stare at the Sun. They're not the boss of you.