The term 'pii' is a play on words of the English term 'pretty', however, by saying 'pii' instead of 'pretty', one projects the idea that they have laced the word with deep sarcasm.
Often used whilst dissing someone's scrap (a.k.a bagging someone out, paying someone out etc etc, for those of you playing at home), 'pii' has its roots in the tongues of Bally students as far as 5 years back. Usage of the word is universal; however, for maximum scrap-dissage effects, one would combine this word with other Bally Slang terms (see examples below).
Most often used in Bally to pay out hectic oge teachers, in particularly Ewna Lady and Conolly.
Guy 2: Pii did my homework... guy.
Conolly: Boys, that's a mulberry tree!
Class: AWWW CHIPS, IS MULBERRY TREE! PII GOOD!
Spiv: DODGY BOYS, EHHHHH! WHERE'S SMOH AH, SHE HAS MY GOLF BALLS. EHHHH!