Green’s Dictionary of Slang

(US) a disgusting or embarrassing person, thing or situation.

1959		Swinging Syllables n.p.: Horror Show—Anything unpleasant.
1964		in Current Sl. (1967) I:4 4/2: Horror show, n. The process whereby one makes a fool of himself.
1972		C. Bukowski Erections, Ejaculations etc. 76: Sometimes it gets to be a real horror show and the only end is death or madness.
1982		W. Safire What’s the Good Word? 124: The advance-decline figures on the New York Stock Exchange are a horror show.
1986		R. Merkin Zombie Jamboree 23: She starts speaking that dumb stuff, and it’s just a horror show [HDAS].
2003		T. Dorsey Stingray Shuffle 217: Serge snapping photos of condemned motels [...] ‘What a horrow show,’ said Lenny.
2015		D. Simon on themarshallproject.org 29 Apr. 🌐 Even in the vernacular of what cops secretly think is fair, this is bullshit, this is a horror show.