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1.
Phrase;

Is when a group of people, usually male, are chillaxing and one of them farts. The d-bag of the group will then proceed to yell "OMG! Someone blew a fattie!"

This is always followed by the rest of the group laughing and pointing and attempting to pass the blame.

People in the general vicinity will also point and laugh; not in an attempt to pass blame, but to make fun of them.
(Group of people are relaxing)
Chris: OH MY GOD! SOMEONE BLEW A FATTIE! (He was the actual one who took partin the action known as "blow a fattie")
(People around him begin to laugh and point and pass blame)

Intelligent Person 1: Whoa, what losers.
Intelligent Person 2: Fo sho.
by fgbm27 February 22, 2007
 
2.
when one flatulates loudly and it has a terrible oder
damn b-ran, did u just blow a fattie.
(nat walks across stage "good god" my tea just changed color)
by Fixx February 14, 2007