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1.
for whatever reason, whether it be a celebration or out of misery, buying a fifth of your favorite alcoholic beverage and proceeding to drink it all in a short amount of time, followed by a blackout until the next day.
"dude, congrats on that A! how are you gonna celebrate it yo?"
"i'm for sure about to head to a party to fifth and forget."

"fml dude"
"i got you buddy, lets fifth and forget, always makes me feel better."
by Shamizard November 21, 2011