This spelling is used to express the amount of shit that they pass. If this were to be pronounced, it would have an extention of "o"s. This would give meaning to how much they have passed.
For a big shit it would be "I just done a Pooooo"
by Cheyne January 25, 2004
poo spelt with 3 o's means a Sam Pooo or a smelly pooo.
'Your a pooo!'
by Jilly mc woooey poooooooooo November 13, 2003