From Longman Dictionary of Contemporary Englishcrack up phrasal verb informal1crack (somebody) upCONTROL to laugh a lot at something, or to make someone laugh a lotEveryone in the class just cracked up.She’s so funny. She cracks me up.2CONTROLto become unable to think or behave sensibly because you have too many problems or too much workI was beginning to think I was cracking up! →crack→ See Verb table
Examples from the Corpus
crack up• Some people can't cope with the death of a loved one, and simply crack up.• I think Paul's cracking up under the strain of work.crack (somebody) up• It used to crack me up.• The cloud is like a magnet so the water goes through the cracks and goes up.• It nearly cracked me up and he could see what it did to me.• Maintenance men could tell whether a pole - wooden or concrete - is dangerously cracked before shinning up it.• It was funny, he cracked me up last night.• All those crack shits shooting up the streets?• Most of the humor consists of watching Shorecrack himself up with his own Valley garble.