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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Top Definition
Something very funny.
When talkin' bout Coke.
"Hahaha, whatta crack up!"
"Yo, Crack up, foo'."
by Diego September 04, 2003

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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 06, 2009

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The Urban Dictionary Mug

Your favorite word on a white mug.

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The Urban Dictionary Mug

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The Urban Dictionary T-Shirt

Soft and offensive. Just like you.

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The Urban Dictionary T-Shirt

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A female pilot flying upside down. An FAA rating obtained by female pilots after they have logged a minimum of 15 hours of inverted flight time.
Sally is a crack up. She can fly better upside down than most pilots can fly right-side up.
by seymour heines February 28, 2008

The Urban Dictionary Mug

Lotsa space for your liquids.

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The Urban Dictionary Mug

Lotsa space for your liquids.

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The Urban Dictionary Mug

Your favorite word on a white mug.

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The Urban Dictionary Mug

One side has the word, one side has the definition. Microwave and dishwasher safe. Lotsa space for your liquids.

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The Urban Dictionary T-Shirt

Soft and offensive. Just like you.

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The Urban Dictionary T-Shirt

Smooth, soft, slim fit American Apparel shirt. Custom printed. 100% fine jersey cotton, except for heather grey (90% cotton).

Buy the t-shirt