Bursting into a prolonged fit of intense, uncontrollable laughter. Instigating this sort of reaction in someone is called "Cracking that person up."
John told me a hilarious joke the other day and I started cracking up.
by lollylollylollyPOP!!! July 24, 2009
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laughing mad hard. Almost to the point of crying. Laughing you split ends off. more than giggleing or laughing
Guy 1: hey, whats wrong wiff aly?

Guy 2: Oh we where talking about how disgusting Michelle's nose is and then she started cracking up

by Petrusha July 1, 2008
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when you cracking up it means you laughing so hard at stupid and retarded shit people say or be doing....and most of the time people is hating you so badly and want to sabotage everything you do and be so evil to you because you so far out their league they cant stand it. and do everything to bring you down and always end up in prison forever or dead the worst way possible like being burn alive.
im cracking up
by Megasus Thrist Jesus Christ April 22, 2022
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Something very funny.
When talkin' bout Coke.
"Hahaha, whatta crack up!"
"Yo, Crack up, foo'."
by Diego September 4, 2003
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Used by stoners when they find something funny, usually said with no emotion.
Vanessa: Did you hear about what happened to Todd?
Ben: Crack up.
by Ark T May 12, 2010
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To burst into loud, hysterical or aggressive verbal abuse. Used primarily in Ireland and the UK. Similar with the American "freak the fuck out," however only used in negative situations.
"Yer wan at the pub cracked up at me when I asked how much she charged for an hour."

"Don't you dare crack up at me! I'm not the one sleepin' with my sister!"
by Lolitaslut May 7, 2009
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