To become insane; to suffer a mental breakdown.(verb)
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Use "crack up" in a sentence
"What ethnological, anthropological, psychological or biological Series of circumstances caused the crew of the Graf Spee to crack up when the men of the Exeter, which was far more badly damaged, stayed calm and went in to fight again?"
"Mark says his grandmother’s so desperately worried that with all this coming on top of Sir Harold’s death and everything she may crack up altogether.”"