A nice pair of peecees tend to get girls thinking about penises and going a bit weak at the knees.
Girl 2: "Oh yeah, he had sexy peecees!"
Both girls: *sigh*
It mainly refers to IBM-compatible x86 systems, often running Microsoft Windows.
The term is believed to be mostly used among Macintosh users.
My Peecee friend: Stop saying 'PeeCee' or I won't give you any beer