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1.
It is mostly used as a greeting or a goodbye. Poop poop is a noun describing someone in your life. So it takes the place of....buddy, pal, dude, brother, sister, father, mother ...etc.
So instead of "Hey Buddy" You would say "Hey Poop Poop" And it is understood that it is meant with a little splash of love.

Normal way
"See ya later Nikki"

The Poop Poop way
"See ya later Poop Poop"
by J McCallum January 14, 2008