What is Crack Up?
1.
Something very funny.
When talkin' bout Coke.
"Hahaha, whatta crack up!"
"Yo, Crack up, foo'."
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2.
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!"
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3.
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.
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