a crash; collision. a breakdown in health, especially a mental breakdown. collapse or disintegration: the crackup of an alliance.

What is crack up laughing?

to laugh with great enthusiasm, or to cause someone to laugh in this way: The stories they told cracked me up.

What does you're a crack up mean?

1. phrasal verb. If someone cracks up, they are under such a lot of emotional strain that they become mentally ill. [informal] She would have cracked up if she hadn't allowed herself some fun.