pigu is the Mandarin word for butt. (confirming someone else's def.)
Other fun related words related to "pi"
pi-gu-yen = anus (literally "butt's eye")
da-pi-gu = spank (literally "hit butt")
fang-pi = fart (litterally "let go of the butt")
gou-pi = nonsense or bullshit (literally dog's butt)
chu-ni-de-gou-pi = (my favorite) out of your dog's butt / blow it out your dog's ass
(i = prounounced as "ee" in all above)
She/he's got nice pigu.
(potentially corrupted) Mandarin Chinese for "ass", often heard on the Joss Whedon show "Firefly".
The stick up your pigu is almost as big as the one he's got.