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1.
A warning of a past event.

Coined by WeezyWaiter(youtube)
Dave: Dude, why didnt you tell me that my ex was gonna be here?
John:Oh right, afterwarning, your ex is gonna be at the party

Dave: Aww man someone robbed my house
John: Oh yea, you forgot to lock your door
Dave: Thanks for the afterwarning
by Wordlizard July 07, 2010