Green’s Dictionary of Slang

nonsense, obsession, tomfoolery.

1958		Mad mag. Sept.–Oct. 4: [poster] Camp Mishigoss meets here.
1971		A. Goldman in N.Y. Mag. 6 Sept. 36: Buttonholing Lenny [...] they plead with him to forget this mishegaas, to release them from this mission impossible.
1978		L. Kramer Faggots 60: His case had entered the international journals as ‘A Famous Son: The Transmission of Psychoneurotic Mishegas from Old World to New’.
1980		S. Steinberg Fairy Tale 43: Or shall I tell her it was just some of your mishegaas? I guess I’d better talk to Uncle Hymie about it.
1998		D. DeLillo Underworld 545: Steiger plays him as a moody and sensitive loner burdened by the whole mishegaas of Russian history.
2001		(con. 1975–6) E. Little Steel Toes 134: Meshugenah, what a mishegoss this is gonna be.
2002		L. Brett Too Many Men 75: ‘To run to somewhere where there is no need to run is a mishegaas.’ [...] A mishegaas, was a stupidity, a madness.
2021		J. Ellroy Widespread Panic 43: ‘Men’s Room Mishegas: Jittery Johnnie Strikes Again’.
2023		(con. 1962) J. Ellroy Enchanters 274: It pertained to the Hoffa/Bobby K. mishigas.