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when one sticks their finger up your own butthole, or anothers butthole, preferably the other gender...but who knows, and when one pulls out such finger, there is butt fecal matter remaining on the once inserted finger, causing the finger to be a "poo poo fingah", then one must point finger upward to initiate the "poo poo fingah"
"Brendan put his finger up Gaysons butthole, then pulled it out, and pointed it in the air, and yelled in a high pitched voice...poo poo fingah"
by Jeff Crehan November 17, 2007