CRACK UP

v. 1. To wreck or be wrecked; smash up. The airplane cracked up in landing. He cracked up his car. 2. informal To become mentally ill under physical or mental overwork or worry. He had kept too busy for years, and when failures came, he cracked up. It seemed to be family problems that made him crack up. 3. Burst into laughter or cause to burst into laughter. That comedian cracks me up.