1) Derived from the words pre- (a prefix), porsche, and unit. Word used to designate a girl with a very proportionate body with slender curves, nice breasts and a nice ass.
It serves as a way of masking the word proportionate so as not to seem obvious in public.
2) A trophy wife. Typically a woman you set yourself up with right after gaining a lump sum of money, and before you buy that Porsche you've always been dreaming of; hence the Pre-Porsche Unit.
Pierre: Yo is your new girl hot?
Shawn: Man you know I'm always after the preporscheunit, so why do you even bother asking?
Zehzeh: Yea me too, I hate brown baggers