Unknown. Popularized by the TV showThe Simpsons where it was one of thecatchphrases ofBart Simpson.

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haveacow (third-person singular simple presenthas a cow,present participlehaving a cow,simple past and past participlehad a cow)

1. (colloquial) To getangry;have a fit.

   My momhad a cow when I came in late.

   • 1959 April 1,The Des Moines Register‎^[1], page 9:

     Dad says I'm too young to go steady and seems to think I'm going to drag a girl up the aisle instead of to a school dance. He won't let me watch rock 'n' roll shows, and he'd "have a cow" if he knew I watched77 Sunset Strip.

   • 1990, “The Call of the Simpsons” (0:12:10 from the start), inThe Simpsons, season 1, episode 7, spoken byHomer Simpson andBart Simpson (Dan Castellaneta andNancy Cartwright):

     "Of all the fates on heaven and earth, why did this one befall me?" "Don'thave a cow, dad."

   • 2007, Julia Spencer-Fleming,In the Bleak Midwinter: A Clare Fergusson and Russ Van Alstyne Mystery, St. Martin's Publishing Group,→ISBN,page69:

     “Pregnant. Holy shit.” “Alyson!” “Oh, Mummy, don'thave a cow.”

   • 2014, Susan Mallery,THE MYSTERIOUS STRANGER, Harlequin,→ISBN,page115:

     “Dammit, Kayla, you're pregnant. Don't pick up a suitcase,” her husband demanded. “It's just a little one.” “Put it down now.” “Don'thave a cow, Patrick. I'm pregnant, not incapacitated.”

2. Used other than figuratively or idiomatically:seehave,‎a,‎cow.

• have kittens