would lose one's head if it weren't attached

“I’m afraid I’ve forgotten my umbrella. Left it on the train.” […] “That man would lose his head if it weren’t attached,” Doris laughed.

1931, Julia K. Duncan [pseudonym; Walter Karig], “A Distasteful Introduction”, in Doris Force at Cloudy Cove or The Old Miser’s Signature, Chicago, Ill.; New York, N.Y.: The Goldsmith Publishing Co., →OCLC, pages 57–58

This mother came in to complain that her boy had lost three hats—one at his riding club, one on the bus on the way home [it is a public service bus and not a school bus], and one on the school play field. […] As we walked out of the office, the principal murmured to me: “That boy would lose his head if it weren’t attached.[…]”

1954 April, Forrest E. Long, “Encouraging Professional Competency Among Teachers”, in The Bulletin of the National Association of Secondary-School Principals, volume 38, number 202, Washington, D.C.: National Association of Secondary-School Principals, page 229

She was a terrible stu­dent, impulsive, hyperac­tive, completely absent-minded and a troublemaker. Her parents humiliated her, calling her a bull in a china shop, saying she would lose her head if it weren’t attached.

1976 June 10, Victoria Graham, “Slow learners present new kind of problem”, in Progress Bulletin, volume 92, number 132, Pomona, Calif., page 18, columns 6–7

When the fun-loving, disorganized Sanguine can't be bothered by the details of keeping up with appointments or getting the children where they need to be on time, the more responsible parent, usually a Melancholy, has to be the family manager, sighing with martyrdom while doing it, “Your mother would lose her head if it weren’t attached” or “Your father never knows which end is up!”

1986, Florence Littauer, “How Can You Bend the Twigs As They Should Go?”, in Discover the Real You by Uncovering the Roots of… Your Personality Tree […], Dallas, Tex.: Word Publishing, →ISBN, page 177

“Mo-ther! Did you pack my white jeans?” Ellen yelled from upstairs. / “No, dear,” Mom answered. As usual she rushed off to help Ellen find them. Ellen would lose her head if it weren’t attached. Half of my life has been spent finding things Ellen has misplaced.

1986, Lou Kassem, chapter 3, in Middle School Blues, New York, N.Y.: Avon Camelot, published September 1987, →ISBN, page 25